Motion vector range derivation for enhanced interpolation filter

ABSTRACT

A method for coding video data is disclosed. The method comprises: obtaining a center motion vector of a coding block; deriving a first motion vector range for the coding block based on the center motion vector and a motion vector spread, wherein the motion vector spread depends on a size of the coding block; if the first motion vector range is at least partially pointing outside a first area including a reference picture, updating the first motion vector range to point within the first area, such that a minimum value or a maximum value of the updated first motion vector range is pointing at a boundary of the first area.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is a continuation of International ApplicationNo. PCT/RU2020/050407, filed on Dec. 31, 2020, which claims the benefitof U.S. Provisional Application No. 62/958,291, filed Jan. 7, 2020. Thedisclosures of the aforementioned applications are hereby incorporatedby reference in their entirety.

TECHNICAL FIELD

Embodiments of the present application generally relate to the field ofpicture processing and more particularly to inter prediction, such asmotion vector range derivation for enhanced interpolation filter.

BACKGROUND

Video coding (video encoding and decoding) is used in a wide range ofdigital video applications, for example broadcast digital TV, videotransmission over internet and mobile networks, real-time conversationalapplications such as video chat, video conferencing, DVD and Blu-raydiscs, video content acquisition and editing systems, and camcorders ofsecurity applications.

The amount of video data needed to depict even a relatively short videocan be substantial, which may result in difficulties when the data is tobe streamed or otherwise communicated across a communications networkwith limited bandwidth capacity. Thus, video data is generallycompressed before being communicated across modern daytelecommunications networks. The size of a video could also be an issuewhen the video is stored on a storage device because memory resourcesmay be limited. Video compression devices often use software and/orhardware at the source to code the video data prior to transmission orstorage, thereby decreasing the quantity of data needed to representdigital video images. The compressed data is then received at thedestination by a video decompression device that decodes the video data.With limited network resources and ever increasing demands of highervideo quality, improved compression and decompression techniques thatimprove compression ratio with little to no sacrifice in picture qualityare desirable.

In Essential Video Coding (EVC), in case of using affine predictionmode, pixel-based affine transform motion compensation can be applied.Specifically, when applying an Enhanced bi-linear Interpolation Filter(EIF), the filtering procedure comprises deriving a pixel-based motionvector field from control point motion vectors, obtaining interpolatedsamples based on the derived motion vectors and filtering the resultwith a high-pass filter. In order to fulfill memory limitationrequirements, a motion vector clipping may have to be applied. However,according to the prior art, a motion vector range is significantlyreduced (sometimes to one point) if the central motion vector is closeto or at the picture boundary. Further, boundary motion vectors may notbe clipped to a range corresponding to the EVC motion vector storageformat.

SUMMARY

Aspects of the present application provide apparatuses and methods forencoding and decoding according to the independent claims.

The foregoing and other objects are achieved by the subject matter ofthe independent claims. Further embodiments are apparent from thedependent claims, the description and the figures.

Particular embodiments are outlined in the attached independent claims,with other embodiments in the dependent claims.

According to a first aspect, the disclosure relates to a method forcoding video data, comprising: obtaining a center motion vector,mv_center, of a coding block, deriving a first motion vector range forthe coding block based on the center motion vector and a motion vectorspread, wherein the motion vector spread depends on a size of the codingblock; if the first motion vector range is at least partially pointingoutside a first area including a reference picture, updating the firstmotion vector range to be pointing within the first area, such that aminimum value and/or a maximum value of the updated first motion vectorrange is pointing at the boundary of the first area, wherein thedifference between the maximum value and the minimum value of theupdated first motion vector range is equal to the minimum of a doublevalue of the motion vector spread and the size of the first area; andperforming pixel-based motion compensation based on the updated firstmotion vector range.

The motion vector is a two-dimensional vector used for inter predictionthat provides an offset from the coordinates in the decoded picture tothe coordinates in a reference picture. A reference picture containssamples that can be used for inter prediction in the decoding process ofsubsequent pictures in decoding order.

Defining horMax-horMin=Min(horMaxPic,horMinPic+2*deviationMV[log2CbWidth−3])−horMinPic=Min(horMaxPic−horMinPic,horMinPic+2*deviationMV[log 2CbWidth−3]−horMinPic)=Min(horMaxPic−horMinPic,2*deviationMV[log 2CbWidth−3]), then

the difference between the maximum value and the minimum of the first MVhorizontal component range of the updated first motion vector range mayrefer to horMax-horMin; the minimum of a double value of the horizontalmotion vector spread and the width of the first area may refer toMin(horMaxPic−horMinPic, 2*deviationMV[log 2 CbWidth−3])=Min(the widthof the first area, doubled horizontal motion vector spread), the widthof the first area may refer to horMaxPic−horMinPic.

Similarly, defining verMax-verMin=Min(verMaxPic, verMinPic+2*deviationMV[log 2 CbHeight−3])−verMinPic=Min(verMaxPic−verMinPic,verMinPic+2*deviationMV[log 2CbHeight−3])−verMinPic)=Min(verMaxPic−verMinPic, 2* deviationMV[log 2CbHeight−3]), then the difference between the maximum value and theminimum of the first MV vertical component range of the updated firstmotion vector range may refer to verMax-verMin; the minimum of a doublevalue of the vertical motion vector spread and the height of the firstarea may refer to Min(verMaxPic−verMinPic, 2*deviationMV[log 2CbHeight−3])=Min(the height of the first area, doubled vertical motionvector spread), the height of the first area may refer toverMaxPic−verMinPic.

Examples of the condition that the motion vector range is at leastpartially pointing outside a boundary of an area including a referencepicture are shown in FIGS. 12 and 13 , in which the motion vector range(spread to the left and right of the central motion vector) is locatedpartially outside the left boundary of the picture. Similar examplesapply to the right, lower and upper boundaries.

The method according to the first aspect avoids a significant reductionof the motion vector range near the picture boundaries.

In an embodiment, the motion vector spread is represented by ahorizontal motion vector spread and/or a vertical motion vector spread,and the horizontal motion vector spread is derived based on the width ofthe coding block, and the vertical motion vector spread is derived basedon the height of the coding block.

In an embodiment, the horizontal motion vector spread is represented bydeviationMV[log 2 CbWidth−3], and the vertical motion vector spread isrepresented by deviationMV[log 2 CbHeight−3], wherein cbWidth andcbHeight represent the width and the height of the coding block.

In an embodiment, the array deviationMV is set equal to {128, 256, 544,1120, 2272}.

In an embodiment, the first motion vector range is represented by afirst MV horizontal component range and/or a first MV vertical componentrange, the first MV horizontal component range comprises a first minimumMV horizontal component value, hor_min and a first maximum MV horizontalcomponent value, hor_max, and the first MV vertical component rangecomprises a first minimum MV vertical component value, ver_min and afirst maximum MV vertical component value, ver_max.

In an embodiment, the method further comprises deriving a second motionvector range based on a size of a picture comprising the coding block,wherein the second motion vector range is represented by a second MVhorizontal component range and/or a second MV vertical component range,the second MV horizontal component range comprises a second minimum MVhorizontal component value, hor_min_pic and a second maximum MVhorizontal component value, hor_max_pic and the second MV verticalcomponent range comprises a second minimum MV vertical component value,ver_min_pic and a second maximum MV vertical component value,ver_max_pic.

In an embodiment, the deriving a second motion vector range based on thesize of a picture comprises: deriving a second motion vector range basedon the size of a picture, a size of the extended area, the coding blockposition inside the picture and the size of the coding block.

In an embodiment, if the first motion vector range is at least partiallypointing outside a first area including a reference picture, updatingthe first motion vector range to be pointing within the first area,comprises: if the first minimum MV horizontal component value, hor_minis less than the second minimum MV horizontal component value,hor_min_pic, setting a updated value of the first minimum MV horizontalcomponent value, hor_min equal to the second minimum MV horizontalcomponent value, hor_min_pic, and deriving a updated value of the firstmaximum MV horizontal component value, hor_max based on a sum of thesecond minimum MV horizontal component value, hor_min_pic and the doublevalue of the horizontal motion vector spread.

Accordingly, the second minimum MV horizontal component value,hor_min_pic corresponds to the left boundary of the first area.

In an embodiment, if the first motion vector range is at least partiallypointing outside a first area including a reference picture, updatingthe first motion vector range to be pointing within the first area,comprises: if the first maximum MV horizontal component value, hor_maxis greater than the second maximum MV horizontal component value,hor_max_pic, setting a updated value of the first maximum MV horizontalcomponent value, hor_max equal to the second maximum MV horizontalcomponent value, hor_max_pic, and deriving a updated value of the firstminimum MV horizontal component value, hor_min based on a subtractionvalue of the second maximum MV horizontal component value, hor_max_picand the doubled value of the horizontal motion vector spread.

Accordingly, the second maximum MV horizontal component value,hor_max_pic corresponds to the right boundary of the first area.

In an embodiment, if the first motion vector range is at least partiallypointing outside a first area including a reference picture, updatingthe first motion vector range to be pointing within the first area,comprises: if the first minimum MV vertical component value, ver_min isless than the second minimum MV vertical component value, ver_min_pic,setting a updated value of the first minimum MV vertical componentvalue, ver_min equal to the second minimum MV vertical component value,ver_min_pic, and deriving a updated value of the first maximum MVvertical component value, ver_max, based on a sum of the second minimumMV vertical component value, ver_min_pic and the double value of thevertical motion vector spread.

Accordingly, the second minimum MV horizontal component value,ver_min_pic corresponds to the upper boundary of the first area.

In an embodiment, if the first motion vector range is at least partiallypointing outside a first area including a reference picture, updatingthe first motion vector range to be pointing within the first area,comprises: if the first maximum MV vertical component value, ver_max isgreater than the second maximum MV vertical component value,ver_max_pic, setting a updated value of the first maximum MV verticalcomponent value, ver_max equal to the second maximum MV verticalcomponent value, ver_max_pic, and deriving a updated value of the firstminimum MV vertical component value, ver_min, based on a subtractionvalue of the second maximum MV vertical component value, ver_max_pic andthe doubled value of the vertical motion vector spread.

Accordingly, the second maximum MV vertical component value, ver_max_piccorresponds to the lower boundary of the first area.

In an embodiment, if the first motion vector range is at least partiallypointing outside a left boundary of the first area, updating thevariables hor_min and hor_max, representing a first MV horizontalcomponent range of the first motion vector range, as:hor_min=hor_min_pic,

hor_max=min (hor_max_pic, hor_min_pic+2*horizontal motion vectorspread); wherein hor_min indicates the updated first minimum MVhorizontal component, and hor_max indicates the updated first maximum MVhorizontal component; wherein hor_min_pic and hor_max_pic, representinga second MV horizontal component range of a second motion vector range;hor_min_pic indicates a second minimum MV horizontal component of thesecond MV horizontal component range, and hor_max_pic indicates a secondmaximum MV horizontal component of the second MV horizontal componentrange, and wherein the second motion vector range depends on a size of apicture comprising the coding block.

Here, if the first minimum MV horizontal component value, hor_min issmaller than the second minimum MV horizontal component value, andhor_min_pic corresponds to the left boundary of the first area.

In an embodiment, if the first motion vector range is at least partiallypointing outside a right boundary of the first area, updating thevariables hor_min and hor_max, representing a first MV horizontalcomponent range of the first motion vector range, as: hor_min=max(hor_min_pic, hor_max_pic−2*horizontal motion vector spread),hor_max=hor_max_pic;

wherein hor_min indicates the updated first minimum MV horizontalcomponent, and hor_max indicates the updated first maximum MV horizontalcomponent; wherein hor_min_pic and hor_max_pic, representing a second MVhorizontal component range of a second motion vector range; hor_min_picindicates a second minimum MV horizontal component of the second MVhorizontal component range, and hor_max_pic indicates a second maximumMV horizontal component of the second MV horizontal component range, andwherein the second motion vector range depends on a size of a picturecomprising the coding block.

Here, if the first maximum MV horizontal component value, hor_max islarger than the second maximum MV horizontal component value, andhor_max_pic corresponds to the right boundary of the first area.

In an embodiment, if the first motion vector range is at least partiallypointing outside an upper boundary of the first area, updating thevariables ver_min and ver_max, representing a first MV verticalcomponent range of the first motion vector range, as:ver_min=ver_min_pic, ver_max=min (ver_max_pic, ver_min_pic+2*verticalmotion vector spread); wherein ver_min indicates the updated firstminimum MV vertical component, and ver_max indicates the updated firstmaximum MV vertical component; wherein ver_min_pic and ver_max_pic,representing a second MV vertical component range of a second motionvector range; ver_min_pic indicates a second minimum MV verticalcomponent of the second MV vertical component range, and ver_max_picindicates a second maximum MV horizontal component of the second MVhorizontal component range, and wherein the second motion vector rangedepends on a size of a picture comprising the coding block.

Here, if the first minimum MV vertical component value, ver_min issmaller than the second minimum MV horizontal component value, andver_min_pic corresponds to the upper boundary of the first area.

In an embodiment, if the first motion vector range is at least partiallylocated outside a lower boundary of the first area, updating thevariables ver_min and ver_max, representing a first MV verticalcomponent range of the first motion vector range, as:

ver_min=max(ver_min_pic,ver_max_pic−2*vertical motion vector spread),ver_max=ver_max_pic;

wherein ver_min indicates the updated first minimum MV verticalcomponent of the first MV vertical component range, and ver_maxindicates the updated first maximum MV vertical component of the firstMV vertical component range; wherein ver_min_pic and ver_max_pic,representing a second MV vertical component range of a second motionvector range; ver_min_pic indicates a second minimum MV verticalcomponent of the second MV vertical component range, and ver_max_picindicates a second maximum MV horizontal component of the second MVhorizontal component range, and wherein the second motion vector rangedepends on a size of a picture comprising the coding block.

Here, if the first maximum MV vertical component value, ver_max islarger than the second maximum MV vertical component value, andver_max_pic corresponds to the lower boundary of the first area. Thesize of the picture may be substantially the same as the size of thereference picture.

In an embodiment, a minimum or maximum value of a horizontal componentof the updated first motion vector range is pointing at a left or rightboundary of the first area, respectively, and/or a minimum or maximumvalue of a vertical component of the updated first motion vector rangeis pointing at an upper or lower boundary of the first area,respectively.

In an embodiment, the first area comprises the reference picture and anextended area surrounding the reference picture.

In an embodiment, a size of the extended area depends on a coding treeunit, CTU, size. A margin may correspond to an area surrounding thereference picture, such that a margin size may correspond to the size ofthe extended area.

In an embodiment, a size of the extended area is 128 pixels.

In an embodiment, the method further comprises: performing a clippingoperation on the updated first motion vector range to be within therange [−217, 217−1]; wherein the performing pixel-based motioncompensation based on the updated first motion vector range, comprises:performing pixel-based motion compensation based on the updated andclipped first motion vector range.

In an embodiment, the variables hor_min, ver_min, hor_max and ver_maxrepresent correspondingly the first minimum MV horizontal componentvalue, the first minimum MV vertical component value, the first maximumMV horizontal component value, and the first maximum MV verticalcomponent value of the updated first motion vector range are clipped asfollows:

hor_max=Clip3(−2¹⁷,2¹⁷−1,hor_max),

ver_max=Clip3(−2¹⁷,2¹⁷−1,ver_max),

hor_min=Clip3(−2¹⁷,2¹⁷−1,hor_min),

ver_min=Clip3(−2¹⁷,2¹⁷−1,ver_min).

In an embodiment, the performing pixel-based motion compensation basedon the updated motion vector range, comprises: performing clippingoperation on a motion vector of a pixel of the coding block to be withina range, to obtain a clipped motion vector, the range depends on theupdated first motion vector range; and performing pixel-based motioncompensation based on the clipped motion vector.

The motion vector of each pixel of the coding block is obtained based onthe affine motion model, and the motion vector of a pixel of theextended area (margin area) surrounding the coding block is obtainedbased on the affine motion model.

In an embodiment, obtaining a center motion vector of a coding block, isperformed according to the following equations:

mv_center[0]=(mvBaseScaled[0]+dX[0]*(cbWidth>>1)+dY[0]*(cbHeight>>1)),

mv_center[1]=(mvBaseScaled[1]+dX[1]*(cbWidth>>1)+dY[1]*(cbHeight>>1));

dX is a horizontal change of the motion vector according to the affinemotion model, dY is a vertical change of the motion vector, according tothe affine motion model, mvBaseScaled is a motion vector correspondingto the top left corner of the coding block, according to the affinemotion model for the coding block, cbWidth and cbHeight are twovariables specifying the width and the height of the coding block.

In an embodiment, deriving a first motion vector range of the codingblock based on the center motion vector and a motion vector spread isperformed according to the following equations:

hor_min=mv_center[0]−deviationMV [log 2CbWidth−3],

ver_min=mv_center[1]−deviationMV [log 2CbHeight−3],

hor_max=mv_center[0]+deviationMV [log 2CbWidth−3],

ver_max=mv_center[1]+deviationMV [log 2CbHeight−3];

wherein:hor_min is the first minimum MV horizontal component value,ver_min is the first minimum MV vertical component value,hor_max is the first maximum MV horizontal component value,ver_max is the first maximum MV vertical component value,mv_center is the center motion vector,wherein mv_center[0] corresponds to the horizontal and mv_center[1]corresponds to the vertical component of the center motion vector.

In an embodiment, deriving a second motion vector range based on thesize of the picture is performed according to the following equations:

hor_max_pic=(pic_width+128−xCb−cbWidth−1)<<5,

ver_max_pic=(pic_height+128−yCb−cbHeight−1)<<5,

hor_min_pic=(−128−xCb)<<5,

ver_min_pic=(−128−yCb)<<5,

wherein:hor_min_pic is the second minimum MV horizontal component value,ver_min_pic is the second minimum MV vertical component value,hor_max_pic is the second maximum MV horizontal component value,ver_max_pic is the second maximum MV vertical component value,(xCb, yCb) is a location of the coding block in full-sample units,cbWidth and cbHeight are two variables specifying the width and theheight of the coding block,pic_width is a width of the picture in samples andpic_height is a height of the picture in samples.

In an embodiment, the pixel-based motion compensation in performed usingEnhanced Interpolation Filter (EIF). Accordingly, EIF may be used for anaffine motion model.

According to a second aspect, the disclosure relates to a codercomprising processing circuitry for carrying out the method according tothe first aspect or any of the embodiments thereof.

In an embodiment, the coder comprises an encoder or a decoder.

According to a third aspect, the disclosure relates to a computerprogram product comprising instructions which, when the program isexecuted by a computer, cause the computer to carry out the methodaccording to the first aspect or any of the embodiments thereof.

According to a fourth aspect, the disclosure relates to a decoder,comprising: one or more processors; and a non-transitorycomputer-readable storage medium coupled to the one or more processorsand storing instructions for execution by the one or more processors,wherein the programming, when executed by the one or more processors,configures the decoder to carry out the method according to the firstaspect or any of the embodiments thereof.

According to a fifth aspect, the disclosure relates to an encoder,comprising: one or more processors; and a non-transitorycomputer-readable storage medium coupled to the one or more processorsand storing instructions for execution by the one or more processors,wherein the programming, when executed by the processors, configures theencoder to carry out the method according to the first aspect or any ofthe embodiments thereof.

The method according to the first aspect can be performed by the coderaccording to the second aspect. Further features and embodiments of themethod according to the first aspect correspond to the features andembodiments of the coder according to the second aspect.

The method according to the first aspect can be performed by the decoderaccording to the fourth aspect. Further features and embodiments of themethod according to the first aspect correspond to the features andembodiments of the decoder according to the fourth aspect.

The method according to the first aspect can be performed by the encoderaccording to the fifth aspect. Further features and embodiments of themethod according to the first aspect correspond to the features andembodiments of the encoder according to the fifth aspect.

The advantages of the coder, decoder and encoder according to the third,fourth, and fifth aspect are the same as those for the method accordingto the first aspect and the corresponding embodiments thereof.

Details of one or more embodiments are set forth in the accompanyingdrawings and the description below. Other features, objects, andadvantages will be apparent from the description, drawings, and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following embodiments of the invention are described in moredetail with reference to the attached figures and drawings, in which:

FIG. 1A is a block diagram showing an example of a video coding systemaccording to an embodiment.

FIG. 1B is a block diagram showing another example of a video codingsystem according to an embodiment.

FIG. 2 is a block diagram showing an example of a video encoderaccording to an embodiment.

FIG. 3 is a block diagram showing an example structure of a videodecoder according to an embodiment.

FIG. 4 is a block diagram illustrating an example of an encodingapparatus or a decoding apparatus.

FIG. 5 is a block diagram illustrating another example of an encodingapparatus or a decoding apparatus.

FIG. 6 is an illustration example of control point based affine motionmodel: 4-parameters and 6-parameters.

FIG. 7 is an illustration example of affine subblock motion vectorfield.

FIG. 8 is an illustration example of the coordinates of corners ofaffine block (subblock) and of intermediate EIF block (subblock).

FIG. 9 is an illustration example of the location of transformed block(subblock) in reference picture and corresponding bounding box.

FIG. 10 is an illustration example of motion vector range updating forcase where central motion vector points outside the reference picture.

FIG. 11 is another illustration example of motion vector range updating,for case where central motion vector points outside the referencepicture, with the real (uncropped) reference area depiction.

FIG. 12 is an illustration example of reducing motion vector range.

FIG. 13 is another illustration example of reducing motion vector range.

FIG. 14 illustrates a comparison between the conventional design and thedesign according to the present disclosure for case where motion vectorrange shrinks to one point near the picture boundaries for theconventional design.

FIG. 15 is a block diagram showing an example structure of a contentsupply system 3100 which realizes a content delivery service.

FIG. 16 is a block diagram showing a structure of an example of aterminal device.

FIG. 17 is a block diagram illustrating the method according to anembodiment.

FIG. 18 is a block diagram illustrating a decoder according to anembodiment.

FIG. 19 is a block diagram illustrating an encoder according to anembodiment.

In the following identical reference signs refer to identical or atleast functionally equivalent features if not explicitly specifiedotherwise.

DETAILED DESCRIPTION

In the following description, reference is made to the accompanyingfigures, which form part of the disclosure, and which show, by way ofillustration, specific aspects of embodiments of the invention orspecific aspects in which embodiments of the present invention may beused. It is understood that embodiments of the invention may be used inother aspects and comprise structural or logical changes not depicted inthe figures. The following detailed description, therefore, is not to betaken in a limiting sense, and the scope of the embodiments of thepresent invention is defined by the appended claims.

For instance, it is understood that a disclosure in connection with adescribed method may also hold true for a corresponding device or systemconfigured to perform the method and vice versa. For example, if one ora plurality of method operations are described, a corresponding devicemay include one or a plurality of units, e.g. functional units, toperform the described one or plurality of method operations (e.g. oneunit performing the one or plurality of operations, or a plurality ofunits each performing one or more of the plurality of operations), evenif such one or more units are not explicitly described or illustrated inthe figures. On the other hand, for example, if a specific apparatus isdescribed based on one or a plurality of units, e.g. functional units, acorresponding method may include one operation to perform thefunctionality of the one or plurality of units (e.g. one operationperforming the functionality of the one or plurality of units, or aplurality of operations each performing the functionality of one or moreof the plurality of units), even if such one or plurality of operationsare not explicitly described or illustrated in the figures. Further, itis understood that the features of the various exemplary embodimentsand/or aspects described herein may be combined with each other, unlessspecifically noted otherwise.

Video coding typically refers to the processing of a sequence ofpictures, which form the video or video sequence. Instead of the term“picture” the term “frame” or “image” may be used as synonyms in thefield of video coding. Video coding (or coding in general) comprises twoparts video encoding and video decoding. Video encoding is performed atthe source side, typically comprising processing (e.g. by compression)the original video pictures to reduce the amount of data required forrepresenting the video pictures (for more efficient storage and/ortransmission). Video decoding is performed at the destination side andtypically comprises the inverse processing compared to the encoder toreconstruct the video pictures. Embodiments referring to “coding” ofvideo pictures (or pictures in general) shall be understood to relate to“encoding” or “decoding” of video pictures or respective videosequences. The combination of the encoding part and the decoding part isalso referred to as CODEC (Coding and Decoding).

In case of lossless video coding, the original video pictures can bereconstructed, i.e. the reconstructed video pictures have the samequality as the original video pictures (assuming no transmission loss orother data loss during storage or transmission). In case of lossy videocoding, further compression, e.g. by quantization, is performed, toreduce the amount of data representing the video pictures, which cannotbe completely reconstructed at the decoder, i.e. the quality of thereconstructed video pictures is lower or worse compared to the qualityof the original video pictures.

Several video coding standards belong to the group of “lossy hybridvideo codecs” (i.e. combine spatial and temporal prediction in thesample domain and 2D transform coding for applying quantization in thetransform domain). Each picture of a video sequence is typicallypartitioned into a set of non-overlapping blocks and the coding istypically performed on a block level. In other words, at the encoder thevideo is typically processed, i.e. encoded, on a block (video block)level, e.g. by using spatial (intra picture) prediction and/or temporal(inter picture) prediction to generate a prediction block, subtractingthe prediction block from the current block (block currentlyprocessed/to be processed) to obtain a residual block, transforming theresidual block and quantizing the residual block in the transform domainto reduce the amount of data to be transmitted (compression), whereas atthe decoder the inverse processing compared to the encoder is applied tothe encoded or compressed block to reconstruct the current block forrepresentation. Furthermore, the encoder duplicates the decoderprocessing loop such that both will generate identical predictions (e.g.intra- and inter predictions) and/or re-constructions for processing,i.e. coding, the subsequent blocks.

In the following embodiments of a video coding system 10, a videoencoder 20 and a video decoder 30 are described based on FIGS. 1 to 3 .

FIG. 1A is a schematic block diagram illustrating an example codingsystem 10, e.g. a video coding system 10 (or short coding system 10)that may utilize techniques of this present application. Video encoder20 (or short encoder 20) and video decoder 30 (or short decoder 30) ofvideo coding system 10 represent examples of devices that may beconfigured to perform techniques in accordance with various examplesdescribed in the present application.

As shown in FIG. 1A, the coding system 10 comprises a source device 12configured to provide encoded picture data 21 e.g. to a destinationdevice 14 for decoding the encoded picture data 13.

The source device 12 comprises an encoder 20, and may additionally,comprise a picture source 16, a pre-processor (or pre-processing unit)18, e.g. a picture pre-processor 18, and a communication interface orcommunication unit 22.

The picture source 16 may comprise or be any kind of picture capturingdevice, for example a camera for capturing a real-world picture, and/orany kind of a picture generating device, for example a computer-graphicsprocessor for generating a computer animated picture, or any kind ofother device for obtaining and/or providing a real-world picture, acomputer generated picture (e.g. a screen content, a virtual reality(VR) picture) and/or any combination thereof (e.g. an augmented reality(AR) picture). The picture source may be any kind of memory or storagestoring any of the aforementioned pictures.

In distinction to the pre-processor 18 and the processing performed bythe pre-processing unit 18, the picture or picture data 17 may also bereferred to as raw picture or raw picture data 17.

Pre-processor 18 is configured to receive the (raw) picture data 17 andto perform pre-processing on the picture data 17 to obtain apre-processed picture 19 or pre-processed picture data 19.Pre-processing performed by the pre-processor 18 may, e.g., comprisetrimming, color format conversion (e.g. from RGB to YCbCr), colorcorrection, or de-noising. It can be understood that the pre-processingunit 18 may be an optional component.

The video encoder 20 is configured to receive the pre-processed picturedata 19 and provide encoded picture data 21 (further details will bedescribed below, e.g., based on FIG. 2 ).

Communication interface 22 of the source device 12 may be configured toreceive the encoded picture data 21 and to transmit the encoded picturedata 21 (or any further processed version thereof) over communicationchannel 13 to another device, e.g. the destination device 14 or anyother device, for storage or direct reconstruction.

The destination device 14 comprises a decoder 30 (e.g. a video decoder30), and may additionally, comprise a communication interface orcommunication unit 28, a post-processor 32 (or post-processing unit 32)and a display device 34.

The communication interface 28 of the destination device 14 isconfigured receive the encoded picture data 21 (or any further processedversion thereof), e.g. directly from the source device 12 or from anyother source, e.g. a storage device, e.g. an encoded picture datastorage device, and provide the encoded picture data 21 to the decoder30.

The communication interface 22 and the communication interface 28 may beconfigured to transmit or receive the encoded picture data 21 or encodeddata 13 via a direct communication link between the source device 12 andthe destination device 14, e.g. a direct wired or wireless connection,or via any kind of network, e.g. a wired or wireless network or anycombination thereof, or any kind of private and public network, or anykind of combination thereof.

The communication interface 22 may be, e.g., configured to package theencoded picture data 21 into an appropriate format, e.g. packets, and/orprocess the encoded picture data using any kind of transmission encodingor processing for transmission over a communication link orcommunication network.

The communication interface 28, forming the counterpart of thecommunication interface 22, may be, e.g., configured to receive thetransmitted data and process the transmission data using any kind ofcorresponding transmission decoding or processing and/or de-packaging toobtain the encoded picture data 21.

Both, communication interface 22 and communication interface 28 may beconfigured as unidirectional communication interfaces as indicated bythe arrow for the communication channel 13 in FIG. TA pointing from thesource device 12 to the destination device 14, or bi-directionalcommunication interfaces, and may be configured, e.g. to send andreceive messages, e.g. to set up a connection, to acknowledge andexchange any other information related to the communication link and/ordata transmission, e.g. encoded picture data transmission.

The decoder 30 is configured to receive the encoded picture data 21 andprovide decoded picture data 31 or a decoded picture 31 (further detailswill be described below, e.g., based on FIG. 3 or FIG. 5 ).

The post-processor 32 of destination device 14 is configured topost-process the decoded picture data 31 (also called reconstructedpicture data), e.g. the decoded picture 31, to obtain post-processedpicture data 33, e.g. a post-processed picture 33. The post-processingperformed by the post-processing unit 32 may comprise, e.g. color formatconversion (e.g. from YCbCr to RGB), color correction, trimming, orre-sampling, or any other processing, e.g. for preparing the decodedpicture data 31 for display, e.g. by display device 34.

The display device 34 of the destination device 14 is configured toreceive the post-processed picture data 33 for displaying the picture,e.g. to a user or viewer. The display device 34 may be or comprise anykind of display for representing the reconstructed picture, e.g. anintegrated or external display or monitor. The displays may, e.g.comprise liquid crystal displays (LCD), organic light emitting diodes(OLED) displays, plasma displays, projectors, micro LED displays, liquidcrystal on silicon (LCoS), digital light processor (DLP) or any kind ofother display.

Although FIG. 1A depicts the source device 12 and the destination device14 as separate devices, embodiments of devices may also comprise both orboth functionalities, the source device 12 or correspondingfunctionality and the destination device 14 or correspondingfunctionality. In such embodiments the source device 12 or correspondingfunctionality and the destination device 14 or correspondingfunctionality may be implemented using the same hardware and/or softwareor by separate hardware and/or software or any combination thereof.

As will be apparent for the skilled person based on the description, theexistence and (exact) split of functionalities of the different units orfunctionalities within the source device 12 and/or destination device 14as shown in FIG. 1A may vary depending on the actual device andapplication.

The encoder 20 (e.g. a video encoder 20) or the decoder 30 (e.g. a videodecoder 30) or both encoder 20 and decoder 30 may be implemented viaprocessing circuitry as shown in FIG. 1B, such as one or moremicroprocessors, digital signal processors (DSPs), application-specificintegrated circuits (ASICs), field-programmable gate arrays (FPGAs),discrete logic, hardware, video coding dedicated or any combinationsthereof. The encoder 20 may be implemented via processing circuitry 46to embody the various modules as discussed with respect to encoder 20 ofFIG. 2 and/or any other encoder system or subsystem described herein.The decoder 30 may be implemented via processing circuitry 46 to embodythe various modules as discussed with respect to decoder 30 of FIG. 3and/or any other decoder system or subsystem described herein. Theprocessing circuitry may be configured to perform the various operationsas discussed later. As shown in FIG. 5 , if the techniques areimplemented partially in software, a device may store instructions forthe software in a suitable, non-transitory computer-readable storagemedium and may execute the instructions in hardware using one or moreprocessors to perform the techniques of this disclosure. Either of videoencoder 20 and video decoder 30 may be integrated as part of a combinedencoder/decoder (CODEC) in a single device, for example, as shown inFIG. 1B.

Source device 12 and destination device 14 may comprise any of a widerange of devices, including any kind of handheld or stationary devices,e.g. notebook or laptop computers, mobile phones, smart phones, tabletsor tablet computers, cameras, desktop computers, set-top boxes,televisions, display devices, digital media players, video gamingconsoles, video streaming devices (such as content services servers orcontent delivery servers), broadcast receiver device, broadcasttransmitter device, or the like and may use no or any kind of operatingsystem. In some cases, the source device 12 and the destination device14 may be equipped for wireless communication. Thus, the source device12 and the destination device 14 may be wireless communication devices.

In some cases, video coding system 10 illustrated in FIG. 1A is merelyan example and the techniques of the present application may apply tovideo coding settings (e.g., video encoding or video decoding) that donot necessarily include any data communication between the encoding anddecoding devices. In other examples, data is retrieved from a localmemory, streamed over a network, or the like. A video encoding devicemay encode and store data to memory, and/or a video decoding device mayretrieve and decode data from memory. In some examples, the encoding anddecoding is performed by devices that do not communicate with oneanother, but simply encode data to memory and/or retrieve and decodedata from memory.

For convenience of description, embodiments of the invention aredescribed herein, for example, by reference to High-Efficiency VideoCoding (HEVC) or to the reference software of Versatile Video coding(VVC), the next generation video coding standard developed by the JointCollaboration Team on Video Coding (JCT-VC) of ITU-T Video CodingExperts Group (VCEG) and ISO/IEC Motion Picture Experts Group (MPEG).One of ordinary skill in the art will understand that embodiments of theinvention are not limited to HEVC or VVC.

Encoder and Encoding Method

FIG. 2 shows a schematic block diagram of an example video encoder 20that is configured to implement the techniques of the presentapplication. In the example of FIG. 2 , the video encoder 20 comprisesan input 201 (or input interface 201), a residual calculation unit 204,a transform processing unit 206, a quantization unit 208, an inversequantization unit 210, and inverse transform processing unit 212, areconstruction unit 214, a loop filter unit 220, a decoded picturebuffer (DPB) 230, a mode selection unit 260, an entropy encoding unit270 and an output 272 (or output interface 272). The mode selection unit260 may include an inter prediction unit 244, an intra prediction unit254 and a partitioning unit 262. Inter prediction unit 244 may include amotion estimation unit and a motion compensation unit (not shown). Avideo encoder 20 as shown in FIG. 2 may also be referred to as hybridvideo encoder or a video encoder according to a hybrid video codec.

The residual calculation unit 204, the transform processing unit 206,the quantization unit 208, the mode selection unit 260 may be referredto as forming a forward signal path of the encoder 20, whereas theinverse quantization unit 210, the inverse transform processing unit212, the reconstruction unit 214, the buffer 216, the loop filter 220,the decoded picture buffer (DPB) 230, the inter prediction unit 244 andthe intra-prediction unit 254 may be referred to as forming a backwardsignal path of the video encoder 20, wherein the backward signal path ofthe video encoder 20 corresponds to the signal path of the decoder (seevideo decoder 30 in FIG. 3 ). The inverse quantization unit 210, theinverse transform processing unit 212, the reconstruction unit 214, theloop filter 220, the decoded picture buffer (DPB) 230, the interprediction unit 244 and the intra-prediction unit 254 are also referredto forming the “built-in decoder” of video encoder 20.

Pictures & Picture Partitioning (Pictures & Blocks)

The encoder 20 may be configured to receive, e.g. via input 201, apicture 17 (or picture data 17), e.g. picture of a sequence of picturesforming a video or video sequence. The received picture or picture datamay also be a pre-processed picture 19 (or pre-processed picture data19). For sake of simplicity the following description refers to thepicture 17. The picture 17 may also be referred to as current picture orpicture to be coded (in particular in video coding to distinguish thecurrent picture from other pictures, e.g. previously encoded and/ordecoded pictures of the same video sequence, i.e. the video sequencewhich also comprises the current picture).

A (digital) picture is or can be regarded as a two-dimensional array ormatrix of samples with intensity values. A sample in the array may alsobe referred to as pixel (short form of picture element) or a pel. Thenumber of samples in horizontal and vertical direction (or axis) of thearray or picture define the size and/or resolution of the picture. Forrepresentation of color, typically three color components are employed,i.e. the picture may be represented or include three sample arrays. InRBG format or color space a picture comprises a corresponding red, greenand blue sample array. However, in video coding each pixel is typicallyrepresented in a luminance and chrominance format or color space, e.g.YCbCr, which comprises a luminance component indicated by Y (sometimesalso L is used instead) and two chrominance components indicated by Cband Cr. The luminance (or short luma) component Y represents thebrightness or grey level intensity (e.g. like in a grey-scale picture),while the two chrominance (or short chroma) components Cb and Crrepresent the chromaticity or color information components. Accordingly,a picture in YCbCr format comprises a luminance sample array ofluminance sample values (Y), and two chrominance sample arrays ofchrominance values (Cb and Cr). Pictures in RGB format may be convertedor transformed into YCbCr format and vice versa, the process is alsoknown as color transformation or conversion. If a picture is monochrome,the picture may comprise only a luminance sample array. Accordingly, apicture may be, for example, an array of luma samples in monochromeformat or an array of luma samples and two corresponding arrays ofchroma samples in 4:2:0, 4:2:2, and 4:4:4 colour format.

Embodiments of the video encoder 20 may comprise a picture partitioningunit (not depicted in FIG. 2 ) configured to partition the picture 17into a plurality of (typically non-overlapping) picture blocks 203.These blocks may also be referred to as root blocks, macro blocks(H.264/AVC) or coding tree blocks (CTB) or coding tree units (CTU)(H.265/HEVC and VVC). The picture partitioning unit may be configured touse the same block size for all pictures of a video sequence and thecorresponding grid defining the block size, or to change the block sizebetween pictures or subsets or groups of pictures, and partition eachpicture into the corresponding blocks.

In further embodiments, the video encoder may be configured to receivedirectly a block 203 of the picture 17, e.g. one, several or all blocksforming the picture 17. The picture block 203 may also be referred to ascurrent picture block or picture block to be coded.

Like the picture 17, the picture block 203 again is or can be regardedas a two-dimensional array or matrix of samples with intensity values(sample values), although of smaller dimension than the picture 17. Inother words, the block 203 may comprise, e.g., one sample array (e.g. aluma array in case of a monochrome picture 17, or a luma or chroma arrayin case of a color picture) or three sample arrays (e.g. a luma and twochroma arrays in case of a color picture 17) or any other number and/orkind of arrays depending on the color format applied. The number ofsamples in horizontal and vertical direction (or axis) of the block 203define the size of block 203. Accordingly, a block may, for example, anM×N (M-column by N-row) array of samples, or an M×N array of transformcoefficients.

Embodiments of the video encoder 20 as shown in FIG. 2 may be configuredto encode the picture 17 block by block, e.g. the encoding andprediction is performed per block 203.

Embodiments of the video encoder 20 as shown in FIG. 2 may be furtherconfigured to partition and/or encode the picture by using slices (alsoreferred to as video slices), wherein a picture may be partitioned intoor encoded using one or more slices (typically non-overlapping), andeach slice may comprise one or more blocks (e.g. CTUs) or one or moregroups of blocks (e.g. tiles (H.265/HEVC and VVC) or bricks (VVC)).

Embodiments of the video encoder 20 as shown in FIG. 2 may be furtherconfigured to partition and/or encode the picture by using slices/tilegroups (also referred to as video tile groups) and/or tiles (alsoreferred to as video tiles), wherein a picture may be partitioned intoor encoded using one or more slices/tile groups (typicallynon-overlapping), and each slice/tile group may comprise, e.g. one ormore blocks (e.g. CTUs) or one or more tiles, wherein each tile, e.g.may be of rectangular shape and may comprise one or more blocks (e.g.CTUs), e.g. complete or fractional blocks.

Residual Calculation

The residual calculation unit 204 may be configured to calculate aresidual block 205 (also referred to as residual 205) based on thepicture block 203 and a prediction block 265 (further details about theprediction block 265 are provided later), e.g. by subtracting samplevalues of the prediction block 265 from sample values of the pictureblock 203, sample by sample (pixel by pixel) to obtain the residualblock 205 in the sample domain.

Transform

The transform processing unit 206 may be configured to apply atransform, e.g. a discrete cosine transform (DCT) or discrete sinetransform (DST), on the sample values of the residual block 205 toobtain transform coefficients 207 in a transform domain. The transformcoefficients 207 may also be referred to as transform residualcoefficients and represent the residual block 205 in the transformdomain.

The transform processing unit 206 may be configured to apply integerapproximations of DCT/DST, such as the transforms specified forH.265/HEVC. Compared to an orthogonal DCT transform, such integerapproximations are typically scaled by a certain factor. In order topreserve the norm of the residual block which is processed by forwardand inverse transforms, additional scaling factors are applied as partof the transform process. The scaling factors are typically chosen basedon certain constraints like scaling factors being a power of two forshift operations, bit depth of the transform coefficients, tradeoffbetween accuracy and implementation costs, etc. Specific scaling factorsare, for example, specified for the inverse transform, e.g. by inversetransform processing unit 212 (and the corresponding inverse transform,e.g. by inverse transform processing unit 312 at video decoder 30) andcorresponding scaling factors for the forward transform, e.g. bytransform processing unit 206, at an encoder 20 may be specifiedaccordingly.

Embodiments of the video encoder 20 (respectively transform processingunit 206) may be configured to output transform parameters, e.g. a typeof transform or transforms, e.g. directly or encoded or compressed viathe entropy encoding unit 270, so that, e.g., the video decoder 30 mayreceive and use the transform parameters for decoding.

Quantization

The quantization unit 208 may be configured to quantize the transformcoefficients 207 to obtain quantized coefficients 209, e.g. by applyingscalar quantization or vector quantization. The quantized coefficients209 may also be referred to as quantized transform coefficients 209 orquantized residual coefficients 209.

The quantization process may reduce the bit depth associated with someor all of the transform coefficients 207. For example, an n-bittransform coefficient may be rounded down to an m-bit Transformcoefficient during quantization, where n is greater than m. The degreeof quantization may be modified by adjusting a quantization parameter(QP). For example for scalar quantization, different scaling may beapplied to achieve finer or coarser quantization. Smaller quantizationstep sizes correspond to finer quantization, whereas larger quantizationstep sizes correspond to coarser quantization. The applicablequantization step size may be indicated by a quantization parameter(QP). The quantization parameter may for example be an index to apredefined set of applicable quantization step sizes. For example, smallquantization parameters may correspond to fine quantization (smallquantization step sizes) and large quantization parameters maycorrespond to coarse quantization (large quantization step sizes) orvice versa. The quantization may include division by a quantization stepsize and a corresponding and/or the inverse dequantization, e.g. byinverse quantization unit 210, may include multiplication by thequantization step size. Embodiments according to some standards, e.g.HEVC, may be configured to use a quantization parameter to determine thequantization step size. Generally, the quantization step size may becalculated based on a quantization parameter using a fixed pointapproximation of an equation including division. Additional scalingfactors may be introduced for quantization and dequantization to restorethe norm of the residual block, which might get modified because of thescaling used in the fixed point approximation of the equation forquantization step size and quantization parameter. In one embodiment,the scaling of the inverse transform and dequantization might becombined. Alternatively, customized quantization tables may be used andsignaled from an encoder to a decoder, e.g. in a bitstream. Thequantization is a lossy operation, wherein the loss increases withincreasing quantization step sizes.

Embodiments of the video encoder 20 (respectively quantization unit 208)may be configured to output quantization parameters (QP), e.g. directlyor encoded via the entropy encoding unit 270, so that, e.g., the videodecoder 30 may receive and apply the quantization parameters fordecoding.

Inverse Quantization

The inverse quantization unit 210 is configured to apply the inversequantization of the quantization unit 208 on the quantized coefficientsto obtain dequantized coefficients 211, e.g. by applying the inverse ofthe quantization scheme applied by the quantization unit 208 based on orusing the same quantization step size as the quantization unit 208. Thedequantized coefficients 211 may also be referred to as dequantizedresidual coefficients 211 and correspond—although typically notidentical to the transform coefficients due to the loss byquantization—to the transform coefficients 207.

Inverse Transform

The inverse transform processing unit 212 is configured to apply theinverse transform of the transform applied by the transform processingunit 206, e.g. an inverse discrete cosine transform (DCT) or inversediscrete sine transform (DST) or other inverse transforms, to obtain areconstructed residual block 213 (or corresponding dequantizedcoefficients 213) in the sample domain. The reconstructed residual block213 may also be referred to as transform block 213.

Reconstruction

The reconstruction unit 214 (e.g. adder or summer 214) is configured toadd the transform block 213 (i.e. reconstructed residual block 213) tothe prediction block 265 to obtain a reconstructed block 215 in thesample domain, e.g. by adding—sample by sample—the sample values of thereconstructed residual block 213 and the sample values of the predictionblock 265.

Filtering

The loop filter unit 220 (or short “loop filter” 220), is configured tofilter the reconstructed block 215 to obtain a filtered block 221, or ingeneral, to filter reconstructed samples to obtain filtered samplevalues. The loop filter unit is, e.g., configured to smooth pixeltransitions, or otherwise improve the video quality. The loop filterunit 220 may comprise one or more loop filters such as a de-blockingfilter, a sample-adaptive offset (SAO) filter or one or more otherfilters, e.g. an adaptive loop filter (ALF), a noise suppression filter(NSF), or any combination thereof. In an example, the loop filter unit220 may comprise a de-blocking filter, a SAO filter and an ALF filter.The order of the filtering process may be the deblocking filter, SAO andALF. In another example, a process called the luma mapping with chromascaling (LMCS) (namely, the adaptive in-loop reshaper) is added. Thisprocess is performed before deblocking. In another example, thedeblocking filter process may be also applied to internal sub-blockedges, e.g. affine sub-blocks edges, ATMVP sub-blocks edges, sub-blocktransform (SBT) edges and intra sub-partition (ISP) edges. Although theloop filter unit 220 is shown in FIG. 2 as being an in loop filter, inother configurations, the loop filter unit 220 may be implemented as apost loop filter. The filtered block 221 may also be referred to asfiltered reconstructed block 221.

Embodiments of the video encoder 20 (respectively loop filter unit 220)may be configured to output loop filter parameters (such as SAO filterparameters or ALF filter parameters or LMCS parameters), e.g. directlyor encoded via the entropy encoding unit 270, so that, e.g., a decoder30 may receive and apply the same loop filter parameters or respectiveloop filters for decoding.

Decoded Picture Buffer

The decoded picture buffer (DPB) 230 may be a memory that storesreference pictures, or in general reference picture data, for encodingvideo data by video encoder 20. The DPB 230 may be formed by any of avariety of memory devices, such as dynamic random access memory (DRAM),including synchronous DRAM (SDRAM), magnetoresistive RAM (MRAM),resistive RAM (RRAM), or other types of memory devices. The decodedpicture buffer (DPB) 230 may be configured to store one or more filteredblocks 221. The decoded picture buffer 230 may be further configured tostore other previously filtered blocks, e.g. previously reconstructedand filtered blocks 221, of the same current picture or of differentpictures, e.g. previously reconstructed pictures, and may providecomplete previously reconstructed, i.e. decoded, pictures (andcorresponding reference blocks and samples) and/or a partiallyreconstructed current picture (and corresponding reference blocks andsamples), for example for inter prediction. The decoded picture buffer(DPB) 230 may be also configured to store one or more unfilteredreconstructed blocks 215, or in general unfiltered reconstructedsamples, e.g. if the reconstructed block 215 is not filtered by loopfilter unit 220, or any other further processed version of thereconstructed blocks or samples.

Mode Selection (Partitioning & Prediction)

The mode selection unit 260 comprises partitioning unit 262,inter-prediction unit 244 and intra-prediction unit 254, and isconfigured to receive or obtain original picture data, e.g. an originalblock 203 (current block 203 of the current picture 17), andreconstructed picture data, e.g. filtered and/or unfilteredreconstructed samples or blocks of the same (current) picture and/orfrom one or a plurality of previously decoded pictures, e.g. fromdecoded picture buffer 230 or other buffers (e.g. line buffer, notshown). The reconstructed picture data is used as reference picture datafor prediction, e.g. inter-prediction or intra-prediction, to obtain aprediction block 265 or predictor 265.

Mode selection unit 260 may be configured to determine or select apartitioning for a current block prediction mode (including nopartitioning) and a prediction mode (e.g. an intra or inter predictionmode) and generate a corresponding prediction block 265, which is usedfor the calculation of the residual block 205 and for the reconstructionof the reconstructed block 215.

Embodiments of the mode selection unit 260 may be configured to selectthe partitioning and the prediction mode (e.g. from those supported byor available for mode selection unit 260), which provide the best matchor in other words the minimum residual (minimum residual means bettercompression for transmission or storage), or a minimum signalingoverhead (minimum signaling overhead means better compression fortransmission or storage), or which considers or balances both. The modeselection unit 260 may be configured to determine the partitioning andprediction mode based on rate distortion optimization (RDO), i.e. selectthe prediction mode which provides a minimum rate distortion. Terms like“best”, “minimum”, “optimum” etc. in this context do not necessarilyrefer to an overall “best”, “minimum”, “optimum”, etc. but may alsorefer to the fulfillment of a termination or selection criterion like avalue exceeding or falling below a threshold or other constraintsleading potentially to a “sub-optimum selection” but reducing complexityand processing time.

In other words, the partitioning unit 262 may be configured to partitiona picture from a video sequence into a sequence of coding tree units(CTUs), and the CTU 203 may be further partitioned into smaller blockpartitions or sub-blocks (which form again blocks), e.g. iterativelyusing quad-tree-partitioning (QT), binary partitioning (BT) ortriple-tree-partitioning (TT) or any combination thereof, and toperform, e.g., the prediction for each of the block partitions orsub-blocks, wherein the mode selection comprises the selection of thetree-structure of the partitioned block 203 and the prediction modes areapplied to each of the block partitions or sub-blocks.

In the following the partitioning (e.g. by partitioning unit 260) andprediction processing (by inter-prediction unit 244 and intra-predictionunit 254) performed by an example video encoder 20 will be explained inmore detail.

Partitioning

The partitioning unit 262 may be configured to partition a picture froma video sequence into a sequence of coding tree units (CTUs), and thepartitioning unit 262 may partition (or split) a coding tree unit (CTU)203 into smaller partitions, e.g. smaller blocks of square orrectangular size. For a picture that has three sample arrays, a CTUconsists of an N×N block of luma samples together with two correspondingblocks of chroma samples. The maximum allowed size of the luma block ina CTU is specified to be 128×128 in the developing versatile videocoding (VVC), but it can be specified to be value rather than 128×128 inthe future, for example, 256×256. The CTUs of a picture may beclustered/grouped as slices/tile groups, tiles or bricks. A tile coversa rectangular region of a picture, and a tile can be divided into one ormore bricks. A brick consists of a number of CTU rows within a tile. Atile that is not partitioned into multiple bricks can be referred to asa brick. However, a brick is a true subset of a tile and is not referredto as a tile. There are two modes of tile groups are supported in VVC,namely the raster-scan slice/tile group mode and the rectangular slicemode. In the raster-scan tile group mode, a slice/tile group contains asequence of tiles in tile raster scan of a picture. In the rectangularslice mode, a slice contains a number of bricks of a picture thatcollectively form a rectangular region of the picture. The bricks withina rectangular slice are in the order of brick raster scan of the slice.These smaller blocks (which may also be referred to as sub-blocks) maybe further partitioned into even smaller partitions. This is alsoreferred to tree-partitioning or hierarchical tree-partitioning, whereina root block, e.g. at root tree-level 0 (hierarchy-level 0, depth 0),may be recursively partitioned, e.g. partitioned into two or more blocksof a next lower tree-level, e.g. nodes at tree-level 1 (hierarchy-level1, depth 1), wherein these blocks may be again partitioned into two ormore blocks of a next lower level, e.g. tree-level 2 (hierarchy-level 2,depth 2), etc. until the partitioning is terminated, e.g. because atermination criterion is fulfilled, e.g. a maximum tree depth or minimumblock size is reached. Blocks which are not further partitioned are alsoreferred to as leaf-blocks or leaf nodes of the tree. A tree usingpartitioning into two partitions is referred to as binary-tree (BT), atree using partitioning into three partitions is referred to asternary-tree (TT), and a tree using partitioning into four partitions isreferred to as quad-tree (QT).

For example, a coding tree unit (CTU) may be or comprise a CTB of lumasamples, two corresponding CTBs of chroma samples of a picture that hasthree sample arrays, or a CTB of samples of a monochrome picture or apicture that is coded using three separate colour planes and syntaxstructures used to code the samples. Correspondingly, a coding treeblock (CTB) may be an N×N block of samples for some value of N such thatthe division of a component into CTBs is a partitioning. A coding unit(CU) may be or comprise a coding block of luma samples, twocorresponding coding blocks of chroma samples of a picture that hasthree sample arrays, or a coding block of samples of a monochromepicture or a picture that is coded using three separate colour planesand syntax structures used to code the samples. Correspondingly a codingblock (CB) may be an M×N block of samples for some values of M and Nsuch that the division of a CTB into coding blocks is a partitioning.

In embodiments, e.g., according to HEVC, a coding tree unit (CTU) may besplit into CUs by using a quad-tree structure denoted as coding tree.The decision whether to code a picture area using inter-picture(temporal) or intra-picture (spatial) prediction is made at the leaf CUlevel. Each leaf CU can be further split into one, two or four PUsaccording to the PU splitting type. Inside one PU, the same predictionprocess is applied and the relevant information is transmitted to thedecoder on a PU basis. After obtaining the residual block by applyingthe prediction process based on the PU splitting type, a leaf CU can bepartitioned into transform units (TUs) according to another quadtreestructure similar to the coding tree for the CU.

In embodiments, e.g., according to the latest video coding standardcurrently in development, which is referred to as Versatile Video Coding(VVC), a combined Quad-tree nested multi-type tree using binary andternary splits segmentation structure for example used to partition acoding tree unit. In the coding tree structure within a coding treeunit, a CU can have either a square or rectangular shape. For example,the coding tree unit (CTU) is first partitioned by a quaternary tree.Then the quaternary tree leaf nodes can be further partitioned by amulti-type tree structure. There are four splitting types in multi-typetree structure, vertical binary splitting (SPLIT_BT_VER), horizontalbinary splitting (SPLIT_BT_HOR), vertical ternary splitting(SPLIT_TT_VER), and horizontal ternary splitting (SPLIT_TT_HOR). Themulti-type tree leaf nodes are called coding units (CUs), and unless theCU is too large for the maximum transform length, this segmentation isused for prediction and transform processing without any furtherpartitioning. This means that, in most cases, the CU, PU and TU have thesame block size in the quadtree with nested multi-type tree coding blockstructure. The exception occurs when maximum supported transform lengthis smaller than the width or height of the colour component of theCU.VVC develops a unique signaling mechanism of the partition splittinginformation in quadtree with nested multi-type tree coding treestructure. In the signalling mechanism, a coding tree unit (CTU) istreated as the root of a quaternary tree and is first partitioned by aquaternary tree structure. Each quaternary tree leaf node (whensufficiently large to allow it) is then further partitioned by amulti-type tree structure. In the multi-type tree structure, a firstflag (mtt_split_cu_flag) is signalled to indicate whether the node isfurther partitioned; when a node is further partitioned, a second flag(mtt_split_cu_vertical_flag) is signalled to indicate the splittingdirection, and then a third flag (mtt_split_cu_binary_flag) is signalledto indicate whether the split is a binary split or a ternary split.Based on the values of mtt_split_cu_vertical_flag andmtt_split_cu_binary_flag, the multi-type tree slitting mode(MttSplitMode) of a CU can be derived by a decoder based on a predefinedrule or a table. It should be noted, for a certain design, for example,64×64 Luma block and 32×32 Chroma pipelining design in VVC hardwaredecoders, TT split is forbidden when either width or height of a lumacoding block is larger than 64, as shown in FIG. 6 . TT split is alsoforbidden when either width or height of a chroma coding block is largerthan 32. The pipelining design will divide a picture into Virtualpipeline data units (VPDUs) which are defined as non-overlapping unitsin a picture. In hardware decoders, successive VPDUs are processed bymultiple pipeline stages simultaneously. The VPDU size is roughlyproportional to the buffer size in most pipeline stages, so it isimportant to keep the VPDU size small. In most hardware decoders, theVPDU size can be set to maximum transform block (TB) size. However, inVVC, ternary tree (TT) and binary tree (BT) partition may lead to theincreasing of VPDUs size.s

In addition, it should be noted that, when a portion of a tree nodeblock exceeds the bottom or right picture boundary, the tree node blockis forced to be split until the all samples of every coded CU arelocated inside the picture boundaries.

As an example, the Intra Sub-Partitions (ISP) tool may divide lumaintra-predicted blocks vertically or horizontally into 2 or 4sub-partitions depending on the block size.

In one example, the mode selection unit 260 of video encoder 20 may beconfigured to perform any combination of the partitioning techniquesdescribed herein.

As described above, the video encoder 20 is configured to determine orselect the best or an optimum prediction mode from a set of (e.g.pre-determined) prediction modes.

The set of prediction modes may comprise, e.g., intra-prediction modesand/or inter-prediction modes.

Intra-Prediction

The set of intra-prediction modes may comprise 35 differentintra-prediction modes, e.g. non-directional modes like DC (or mean)mode and planar mode, or directional modes, e.g. as defined in HEVC, ormay comprise 67 different intra-prediction modes, e.g. non-directionalmodes like DC (or mean) mode and planar mode, or directional modes, e.g.as defined for VVC. As an example, several conventional angular intraprediction modes are adaptively replaced with wide-angle intraprediction modes for the non-square blocks, e.g. as defined in VVC. Asanother example, to avoid division operations for DC prediction, onlythe longer side is used to compute the average for non-square blocks.And, the results of intra prediction of planar mode may be furthermodified by a position dependent intra prediction combination (PDPC)method.

The intra-prediction unit 254 is configured to use reconstructed samplesof neighboring blocks of the same current picture to generate anintra-prediction block 265 according to an intra-prediction mode of theset of intra-prediction modes.

The intra prediction unit 254 (or in general the mode selection unit260) is further configured to output intra-prediction parameters (or ingeneral information indicative of the selected intra prediction mode forthe block) to the entropy encoding unit 270 in form of syntax elements266 for inclusion into the encoded picture data 21, so that, e.g., thevideo decoder 30 may receive and use the prediction parameters fordecoding.

Inter-Prediction

The set of (or possible) inter-prediction modes depends on the availablereference pictures (i.e. previous at least partially decoded pictures,e.g. stored in DBP 230) and other inter-prediction parameters, e.g.whether the whole reference picture or only a part, e.g. a search windowarea around the area of the current block, of the reference picture isused for searching for a best matching reference block, and/or e.g.whether pixel interpolation is applied, e.g. half/semi-pel, quarter-peland/or 1/16 pel interpolation, or not.

Additional to the above prediction modes, skip mode, direct mode and/orother inter prediction mode may be applied.

For example, Extended merge prediction, the merge candidate list of suchmode is constructed by including the following five types of candidatesin order: Spatial MVP from spatial neighbor CUs, Temporal MVP fromcollocated CUs, History-based MVP from an FIFO table, Pairwise averageMVP and Zero MVs. And a bilateral-matching based decoder side motionvector refinement (DMVR) may be applied to increase the accuracy of theMVs of the merge mode. Merge mode with MVD (MMVD), which comes frommerge mode with motion vector differences. A MMVD flag is signaled rightafter sending a skip flag and merge flag to specify whether MMVD mode isused for a CU. And a CU-level adaptive motion vector resolution (AMVR)scheme may be applied. AMVR allows MVD of the CU to be coded indifferent precision. Dependent on the prediction mode for the currentCU, the MVDs of the current CU can be adaptively selected. When a CU iscoded in merge mode, the combined inter/intra prediction (CIIP) mode maybe applied to the current CU. Weighted averaging of the inter and intraprediction signals is performed to obtain the CIIP prediction. Affinemotion compensated prediction, the affine motion field of the block isdescribed by motion information of two control point (4-parameter) orthree control point motion vectors (6-parameter). Subblock-basedtemporal motion vector prediction (SbTMVP), which is similar to thetemporal motion vector prediction (TMVP) in HEVC, but predicts themotion vectors of the sub-CUs within the current CU. Bi-directionaloptical flow (BDOF), previously referred to as BIO, is a simpler versionthat requires much less computation, especially in terms of number ofmultiplications and the size of the multiplier. Triangle partition mode,in such a mode, a CU is split evenly into two triangle-shapedpartitions, using either the diagonal split or the anti-diagonal split.Besides, the bi-prediction mode is extended beyond simple averaging toallow weighted averaging of the two prediction signals.

The inter prediction unit 244 may include a motion estimation (ME) unitand a motion compensation (MC) unit (both not shown in FIG. 2 ). Themotion estimation unit may be configured to receive or obtain thepicture block 203 (current picture block 203 of the current picture 17)and a decoded picture 231, or at least one or a plurality of previouslyreconstructed blocks, e.g. reconstructed blocks of one or a plurality ofother/different previously decoded pictures 231, for motion estimation.E.g. a video sequence may comprise the current picture and thepreviously decoded pictures 231, or in other words, the current pictureand the previously decoded pictures 231 may be part of or form asequence of pictures forming a video sequence.

The encoder 20 may, e.g., be configured to select a reference block froma plurality of reference blocks of the same or different pictures of theplurality of other pictures and provide a reference picture (orreference picture index) and/or an offset (spatial offset) between theposition (x, y coordinates) of the reference block and the position ofthe current block as inter prediction parameters to the motionestimation unit. This offset is also called motion vector (MV).

The motion compensation unit is configured to obtain, e.g. receive, aninter prediction parameter and to perform inter prediction based on orusing the inter prediction parameter to obtain an inter prediction block265. Motion compensation, performed by the motion compensation unit, mayinvolve fetching or generating the prediction block based on themotion/block vector determined by motion estimation, possibly performinginterpolations to sub-pixel precision. Interpolation filtering maygenerate additional pixel samples from known pixel samples, thuspotentially increasing the number of candidate prediction blocks thatmay be used to code a picture block. Upon receiving the motion vectorfor the PU of the current picture block, the motion compensation unitmay locate the prediction block to which the motion vector points in oneof the reference picture lists.

The motion compensation unit may also generate syntax elementsassociated with the blocks and video slices for use by video decoder 30in decoding the picture blocks of the video slice. In addition or as analternative to slices and respective syntax elements, tile groups and/ortiles and respective syntax elements may be generated or used.

Entropy Coding

The entropy encoding unit 270 is configured to apply, for example, anentropy encoding algorithm or scheme (e.g. a variable length coding(VLC) scheme, an context adaptive VLC scheme (CAVLC), an arithmeticcoding scheme, a binarization, a context adaptive binary arithmeticcoding (CABAC), syntax-based context-adaptive binary arithmetic coding(SBAC), probability interval partitioning entropy (PIPE) coding oranother entropy encoding methodology or technique) or bypass (nocompression) on the quantized coefficients 209, inter predictionparameters, intra prediction parameters, loop filter parameters and/orother syntax elements to obtain encoded picture data 21 which can beoutput via the output 272, e.g. in the form of an encoded bitstream 21,so that, e.g., the video decoder 30 may receive and use the parametersfor decoding. The encoded bitstream 21 may be transmitted to videodecoder 30, or stored in a memory for later transmission or retrieval byvideo decoder 30.

Other structural variations of the video encoder 20 can be used toencode the video stream. For example, a non-transform based encoder 20can quantize the residual signal directly without the transformprocessing unit 206 for certain blocks or frames. In anotherimplementation, an encoder 20 can have the quantization unit 208 and theinverse quantization unit 210 combined into a single unit.

Decoder and Decoding Method

FIG. 3 shows an example of a video decoder 30 that is configured toimplement the techniques of this present application. The video decoder30 is configured to receive encoded picture data 21 (e.g. encodedbitstream 21), e.g. encoded by encoder 20, to obtain a decoded picture331. The encoded picture data or bitstream comprises information fordecoding the encoded picture data, e.g. data that represents pictureblocks of an encoded video slice (and/or tile groups or tiles) andassociated syntax elements.

In the example of FIG. 3 , the decoder 30 comprises an entropy decodingunit 304, an inverse quantization unit 310, an inverse transformprocessing unit 312, a reconstruction unit 314 (e.g. a summer 314), aloop filter 320, a decoded picture buffer (DBP) 330, a mode applicationunit 360, an inter prediction unit 344 and an intra prediction unit 354.Inter prediction unit 344 may be or include a motion compensation unit.Video decoder 30 may, in some examples, perform a decoding passgenerally reciprocal to the encoding pass described with respect tovideo encoder 100 from FIG. 2 .

As explained with regard to the encoder 20, the inverse quantizationunit 210, the inverse transform processing unit 212, the reconstructionunit 214, the loop filter 220, the decoded picture buffer (DPB) 230, theinter prediction unit 344 and the intra prediction unit 354 are alsoreferred to as forming the “built-in decoder” of video encoder 20.Accordingly, the inverse quantization unit 310 may be identical infunction to the inverse quantization unit 110, the inverse transformprocessing unit 312 may be identical in function to the inversetransform processing unit 212, the reconstruction unit 314 may beidentical in function to reconstruction unit 214, the loop filter 320may be identical in function to the loop filter 220, and the decodedpicture buffer 330 may be identical in function to the decoded picturebuffer 230. Therefore, the explanations provided for the respectiveunits and functions of the video 20 encoder apply correspondingly to therespective units and functions of the video decoder 30.

Entropy Decoding

The entropy decoding unit 304 is configured to parse the bitstream 21(or in general encoded picture data 21) and perform, for example,entropy decoding to the encoded picture data 21 to obtain, e.g.,quantized coefficients 309 and/or decoded coding parameters (not shownin FIG. 3 ), e.g. any or all of inter prediction parameters (e.g.reference picture index and motion vector), intra prediction parameter(e.g. intra prediction mode or index), transform parameters,quantization parameters, loop filter parameters, and/or other syntaxelements. Entropy decoding unit 304 may be configured to apply thedecoding algorithms or schemes corresponding to the encoding schemes asdescribed with regard to the entropy encoding unit 270 of the encoder20. Entropy decoding unit 304 may be further configured to provide interprediction parameters, intra prediction parameter and/or other syntaxelements to the mode application unit 360 and other parameters to otherunits of the decoder 30. Video decoder 30 may receive the syntaxelements at the video slice level and/or the video block level. Inaddition or as an alternative to slices and respective syntax elements,tile groups and/or tiles and respective syntax elements may be receivedand/or used.

Inverse Quantization

The inverse quantization unit 310 may be configured to receivequantization parameters (QP) (or in general information related to theinverse quantization) and quantized coefficients from the encodedpicture data 21 (e.g. by parsing and/or decoding, e.g. by entropydecoding unit 304) and to apply based on the quantization parameters aninverse quantization on the decoded quantized coefficients 309 to obtaindequantized coefficients 311, which may also be referred to as transformcoefficients 311. The inverse quantization process may include use of aquantization parameter determined by video encoder 20 for each videoblock in the video slice (or tile or tile group) to determine a degreeof quantization and, likewise, a degree of inverse quantization thatshould be applied.

Inverse Transform

Inverse transform processing unit 312 may be configured to receivedequantized coefficients 311, also referred to as transform coefficients311, and to apply a transform to the dequantized coefficients 311 inorder to obtain reconstructed residual blocks 213 in the sample domain.The reconstructed residual blocks 213 may also be referred to astransform blocks 313. The transform may be an inverse transform, e.g.,an inverse DCT, an inverse DST, an inverse integer transform, or aconceptually similar inverse transform process. The inverse transformprocessing unit 312 may be further configured to receive transformparameters or corresponding information from the encoded picture data 21(e.g. by parsing and/or decoding, e.g. by entropy decoding unit 304) todetermine the transform to be applied to the dequantized coefficients311.

Reconstruction

The reconstruction unit 314 (e.g. adder or summer 314) may be configuredto add the reconstructed residual block 313, to the prediction block 365to obtain a reconstructed block 315 in the sample domain, e.g. by addingthe sample values of the reconstructed residual block 313 and the samplevalues of the prediction block 365.

Filtering

The loop filter unit 320 (either in the coding loop or after the codingloop) is configured to filter the reconstructed block 315 to obtain afiltered block 321, e.g. to smooth pixel transitions, or otherwiseimprove the video quality. The loop filter unit 320 may comprise one ormore loop filters such as a de-blocking filter, a sample-adaptive offset(SAO) filter or one or more other filters, e.g. an adaptive loop filter(ALF), a noise suppression filter (NSF), or any combination thereof. Inan example, the loop filter unit 220 may comprise a de-blocking filter,a SAO filter and an ALF filter. The order of the filtering process maybe the deblocking filter, SAO and ALF. In another example, a processcalled the luma mapping with chroma scaling (LMCS) (namely, the adaptivein-loop reshaper) is added. This process is performed before deblocking.In another example, the deblocking filter process may be also applied tointernal sub-block edges, e.g. affine sub-blocks edges, ATMVP sub-blocksedges, sub-block transform (SBT) edges and intra sub-partition (ISP)edges. Although the loop filter unit 320 is shown in FIG. 3 as being anin loop filter, in other configurations, the loop filter unit 320 may beimplemented as a post loop filter.

Decoded Picture Buffer

The decoded video blocks 321 of a picture are then stored in decodedpicture buffer 330, which stores the decoded pictures 331 as referencepictures for subsequent motion compensation for other pictures and/orfor output respectively display.

The decoder 30 is configured to output the decoded picture 311, e.g. viaoutput 312, for presentation or viewing to a user.

Prediction

The inter prediction unit 344 may be identical to the inter predictionunit 244 (in particular to the motion compensation unit) and the intraprediction unit 354 may be identical to the inter prediction unit 254 infunction, and performs split or partitioning decisions and predictionbased on the partitioning and/or prediction parameters or respectiveinformation received from the encoded picture data 21 (e.g. by parsingand/or decoding, e.g. by entropy decoding unit 304). Mode applicationunit 360 may be configured to perform the prediction (intra or interprediction) per block based on reconstructed pictures, blocks orrespective samples (filtered or unfiltered) to obtain the predictionblock 365.

When the video slice is coded as an intra coded (I) slice, intraprediction unit 354 of mode application unit 360 is configured togenerate prediction block 365 for a picture block of the current videoslice based on a signaled intra prediction mode and data from previouslydecoded blocks of the current picture. When the video picture is codedas an inter coded (i.e., B, or P) slice, inter prediction unit 344 (e.g.motion compensation unit) of mode application unit 360 is configured toproduce prediction blocks 365 for a video block of the current videoslice based on the motion vectors and other syntax elements receivedfrom entropy decoding unit 304. For inter prediction, the predictionblocks may be produced from one of the reference pictures within one ofthe reference picture lists. Video decoder 30 may construct thereference frame lists, List 0 and List 1, using default constructiontechniques based on reference pictures stored in DPB 330. The same orsimilar may be applied for or by embodiments using tile groups (e.g.video tile groups) and/or tiles (e.g. video tiles) in addition oralternatively to slices (e.g. video slices), e.g. a video may be codedusing I, P or B tile groups and/or tiles.

Mode application unit 360 is configured to determine the predictioninformation for a video block of the current video slice by parsing themotion vectors or related information and other syntax elements, anduses the prediction information to produce the prediction blocks for thecurrent video block being decoded. For example, the mode applicationunit 360 uses some of the received syntax elements to determine aprediction mode (e.g., intra or inter prediction) used to code the videoblocks of the video slice, an inter prediction slice type (e.g., Bslice, P slice, or GPB slice), construction information for one or moreof the reference picture lists for the slice, motion vectors for eachinter encoded video block of the slice, inter prediction status for eachinter coded video block of the slice, and other information to decodethe video blocks in the current video slice. The same or similar may beapplied for or by embodiments using tile groups (e.g. video tile groups)and/or tiles (e.g. video tiles) in addition or alternatively to slices(e.g. video slices), e.g. a video may be coded using I, P or B tilegroups and/or tiles.

Embodiments of the video decoder 30 as shown in FIG. 3 may be configuredto partition and/or decode the picture by using slices (also referred toas video slices), wherein a picture may be partitioned into or decodedusing one or more slices (typically non-overlapping), and each slice maycomprise one or more blocks (e.g. CTUs) or one or more groups of blocks(e.g. tiles (H.265/HEVC and VVC) or bricks (VVC)).

Embodiments of the video decoder 30 as shown in FIG. 3 may be configuredto partition and/or decode the picture by using slices/tile groups (alsoreferred to as video tile groups) and/or tiles (also referred to asvideo tiles), wherein a picture may be partitioned into or decoded usingone or more slices/tile groups (typically non-overlapping), and eachslice/tile group may comprise, e.g. one or more blocks (e.g. CTUs) orone or more tiles, wherein each tile, e.g. may be of rectangular shapeand may comprise one or more blocks (e.g. CTUs), e.g. complete orfractional blocks.

Other variations of the video decoder 30 can be used to decode theencoded picture data 21. For example, the decoder 30 can produce theoutput video stream without the loop filtering unit 320. For example, anon-transform based decoder 30 can inverse-quantize the residual signaldirectly without the inverse-transform processing unit 312 for certainblocks or frames. In another embodiment, the video decoder 30 can havethe inverse-quantization unit 310 and the inverse-transform processingunit 312 combined into a single unit.

It should be understood that, in the encoder 20 and the decoder 30, aprocessing result of a current step may be further processed and thenoutput to the next step. For example, after interpolation filtering,motion vector derivation or loop filtering, a further operation, such asClip or shift, may be performed on the processing result of theinterpolation filtering, motion vector derivation or loop filtering.

It should be noted that further operations may be applied to the derivedmotion vectors of current block (including but not limit to controlpoint motion vectors of affine mode, sub-block motion vectors in affine,planar, ATMVP modes, temporal motion vectors, and so on). For example,the value of motion vector is constrained to a predefined rangeaccording to its representing bit. If the representing bit of motionvector is bitDepth, then the range is −2{circumflex over( )}(bitDepth−1)˜2{circumflex over ( )}(bitDepth−1)−1, where“{circumflex over ( )}” means exponentiation. For example, if bitDepthis set equal to 16, the range is −32768˜32767; if bitDepth is set equalto 18, the range is −131072˜131071. For example, the value of thederived motion vector (e.g. the MVs of four 4×4 sub-blocks within one8×8 block) is constrained such that the max difference between integerparts of the four 4×4 sub-block MVs is no more than N pixels, such as nomore than 1 pixel. Here provides two methods for constraining the motionvector according to the bitDepth.

FIG. 4 is a schematic diagram of a video coding device 400 according toan embodiment of the disclosure. The video coding device 400 is suitablefor implementing the disclosed embodiments as described herein. In anembodiment, the video coding device 400 may be a decoder such as videodecoder 30 of FIG. 1A or an encoder such as video encoder 20 of FIG. 1A.

The video coding device 400 comprises ingress ports 410 (or input ports410) and receiver units (Rx) 420 for receiving data; a processor, logicunit, or central processing unit (CPU) 430 to process the data;transmitter units (Tx) 440 and egress ports 450 (or output ports 450)for transmitting the data; and a memory 460 for storing the data. Thevideo coding device 400 may also comprise optical-to-electrical (OE)components and electrical-to-optical (EO) components coupled to theingress ports 410, the receiver units 420, the transmitter units 440,and the egress ports 450 for egress or ingress of optical or electricalsignals.

The processor 430 is implemented by hardware and software. The processor430 may be implemented as one or more CPU chips, cores (e.g., as amulti-core processor), FPGAs, ASICs, and DSPs. The processor 430 is incommunication with the ingress ports 410, receiver units 420,transmitter units 440, egress ports 450, and memory 460. The processor430 comprises a coding module 470. The coding module 470 implements thedisclosed embodiments described above. For instance, the coding module470 implements, processes, prepares, or provides the various codingoperations. The inclusion of the coding module 470 therefore provides asubstantial improvement to the functionality of the video coding device400 and effects a transformation of the video coding device 400 to adifferent state. Alternatively, the coding module 470 is implemented asinstructions stored in the memory 460 and executed by the processor 430.

The memory 460 may comprise one or more disks, tape drives, andsolid-state drives and may be used as an over-flow data storage device,to store programs when such programs are selected for execution, and tostore instructions and data that are read during program execution. Thememory 460 may be, for example, volatile and/or non-volatile and may bea read-only memory (ROM), random access memory (RAM), ternarycontent-addressable memory (TCAM), and/or static random-access memory(SRAM).

FIG. 5 is a simplified block diagram of an apparatus 500 that may beused as either or both of the source device 12 and the destinationdevice 14 from FIG. 1 according to an exemplary embodiment.

A processor 502 in the apparatus 500 can be a central processing unit.Alternatively, the processor 502 can be any other type of device, ormultiple devices, capable of manipulating or processing informationnow-existing or hereafter developed. Although the disclosed embodimentscan be practiced with a single processor as shown, e.g., the processor502, advantages in speed and efficiency can be achieved using more thanone processor.

A memory 504 in the apparatus 500 can be a read only memory (ROM) deviceor a random access memory (RAM) device in an implementation. Any othersuitable type of storage device can be used as the memory 504. Thememory 504 can include code and data 506 that is accessed by theprocessor 502 using a bus 512. The memory 504 can further include anoperating system 508 and application programs 510, the applicationprograms 510 including at least one program that permits the processor502 to perform the methods described here. For example, the applicationprograms 510 can include applications 1 through N, which further includea video coding application that performs the methods described here.

The apparatus 500 can also include one or more output devices, such as adisplay 518. The display 518 may be, in one example, a touch sensitivedisplay that combines a display with a touch sensitive element that isoperable to sense touch inputs. The display 518 can be coupled to theprocessor 502 via the bus 512.

Although depicted here as a single bus, the bus 512 of the apparatus 500can be composed of multiple buses. Further, the secondary storage 514can be directly coupled to the other components of the apparatus 500 orcan be accessed via a network and can comprise a single integrated unitsuch as a memory card or multiple units such as multiple memory cards.The apparatus 500 can thus be implemented in a wide variety ofconfigurations.

1 Background

In the following, background information for the present disclosure ispresented.

1.1 Affine Motion Compensated Prediction

In ITU-T H.265, only translation motion model is applied for motioncompensation prediction (MCP). While in the real world, there are manykinds of motion, e.g. zoom in/out, rotation, perspective motions and theother irregular motions. In the EVC, a block-based affine transformmotion compensation prediction is applied. As shown at FIG. 6 , theaffine motion field of the block is described by motion information oftwo control point (4-parameter) or three control point motion vectors(CPMV) (6-parameter).

1.1.1 General Equations for Motion Vector Derivation

The general equation for calculation motion vector at sample location(x, y) is:

$\begin{matrix}\left\{ \begin{matrix}{{mv}_{x} = {{{dHorX}*x} + {{dVerX}*y} + {mv}_{0x}}} \\{{mv}_{y} = {{{dHorY}*x} + {{dVerY}*y} + {mv}_{0y}}}\end{matrix} \right. & \left( {1 - 1} \right)\end{matrix}$

For 4-parameter affine motion model, motion vector at sample location(x, y) is derived as:

$\begin{matrix}\left\{ \begin{matrix}{{mv}_{x} = {{\frac{{mv}_{1x} - {mv}_{0x}}{W}x} + {\frac{{mv}_{0y} - {mv}_{1y}}{W}y} + {mv}_{0x}}} \\{{mv}_{y} = {{\frac{{mv}_{1y} - {mv}_{0y}}{W}x} + {\frac{{mv}_{1x} - {mv}_{0x}}{W}y} + {mv}_{0y}}}\end{matrix} \right. & \left( {1 - 2} \right)\end{matrix}$

For 6-parameter affine motion model, motion vector at sample location(x, y) is derived as:

$\begin{matrix}\left\{ \begin{matrix}{{mv}_{x} = {{\frac{{mv}_{1x} - {mv}_{0x}}{W}x} + {\frac{{mv}_{2x} - {mv}_{0x}}{H}y} + {mv}_{0x}}} \\{{mv}_{y} = {{\frac{{mv}_{1y} - {mv}_{0y}}{W}x} + {\frac{{mv}_{2y} - {mv}_{0y}}{H}y} + {mv}_{0y}}}\end{matrix} \right. & \left( {1 - 3} \right)\end{matrix}$

Where (mv_(0x), mv_(0y)) is motion vector of the top-left corner controlpoint, (mv_(1x), mv_(1y)) is motion vector of the top-right cornercontrol point, and (mv_(2x), mv_(2y)) is motion vector of thebottom-left corner control point.

For case of using 6-parameter affine motion model

$\begin{matrix}{{dHorX} = \frac{{mv}_{1x} - {mv}_{0x}}{W}} & \left( {1 - 4} \right)\end{matrix}$ $\begin{matrix}{{{dHorY} = \frac{{mv}_{1y} - {mv}_{0y}}{W}},} & \left( {1 - 5} \right)\end{matrix}$ $\begin{matrix}{{{dVerX} = \frac{{mv}_{2x} - {mv}_{0x}}{H}},} & \left( {1 - 6} \right)\end{matrix}$ $\begin{matrix}{{dVerY} = \frac{{mv}_{2y} - {mv}_{0y}}{H}} & \left( {1 - 7} \right)\end{matrix}$

For case of using 4-parameter affine motion model,

$\begin{matrix}{{{dHorX} = \frac{{mv}_{1x} - {mv}_{0x}}{W}},} & \left( {1 - 8} \right)\end{matrix}$ $\begin{matrix}{{{dHorY} = \frac{{mv}_{1y} - {mv}_{0y}}{W}},} & \left( {1 - 9} \right)\end{matrix}$ $\begin{matrix}{{{dVerX} = {- {dHorY}}},} & \left( {1 - 10} \right)\end{matrix}$ $\begin{matrix}{{dVerY} = {{dHorX}.}} & \left( {1 - 11} \right)\end{matrix}$

As done for translational motion inter prediction, there are also twoaffine motion inter prediction modes: affine merge mode and affine AMVPmode.

1.1.2 Memory Bandwidth Calculation

Memory bandwidth is calculated as a reference block to current blockarea ratio. For example, for 8×8 bi-predictive block in case of usageinterpolation filter with T taps, the reference area value is Sr isequal to 2(8+T−1)(8+T−1), block area Sb is equal to 8*8. So memorybandwidth is

${MB}_{8 \times 8} = {\frac{2\left( {8 + T - 1} \right)\left( {8 + T - 1} \right)}{64}.}$

For 8-tap DCTIF that is used in ITU-T H.265, VVC and EVC,

${MB}_{8 \times 8} = {\frac{2*15*15}{64} = {7.03125.}}$

1.2 Block Based Affine Transform Prediction

In order to simplify the motion compensation prediction, block basedaffine transform prediction is applied. To derive motion vector of each8×8 luma sub-block, the motion vector of the center sample of eachsub-block, as shown in FIG. 7 , is calculated according to aboveequations, and rounded to 1/16 fraction accuracy. Then the motioncompensation interpolation filters are applied, to generate theprediction of each sub-block with derived motion vector. The sub-blocksize of chroma-components is set to be 4×4.

1.2.1 Block Based Affine Transform Prediction with 8×8 Subblocks

Subblock affine motion compensation with minimal subblock size 8×8 ismuch more hardware friendly than affine motion compensation with minimalsubblock size 4×4. There are at least three reasons for that.

-   -   1. Memory bandwidth. Affine motion compensation with minimal        subblock size 8×8 does not increase the memory bandwidth        compared to ITU-T H.265, because 8×8 bi-predictive blocks are        the worst case for ITU-T H.265 in terms of memory bandwidth        calculation. In EVC 8×8 bi-predictive blocks also does not        change the worst case in terms of memory bandwidth (8×4/4×8        bi-predictive blocks are the worst case in EVC 3.0 and 4×16/16×4        blocks are going to be the worst case in EVC 4.0). Basically 8×8        bi-predictive blocks can occur in regular inter prediction both        in EVC and ITU-T H.265, so affine subblock motion compensation        with such minimal block size does not increase complexity of        motion compensation.    -   2. Number of multiplications. Motion compensation for 8×8        subblock requires much less number of multiplications than        motion compensation of four 4×4 subblocks.    -   3. Memory access. In some embodiments no less than 16 samples        can be read. From this perspective 8×8 blocks that in case of        usage 8-tap DCTIF takes (8+8−1)*(8+8−1) reference samples        utilize memory much more efficient than 4×4 blocks.

However subblock affine motion compensation with minimal subblock size8×8 is much provides significant performance drop in comparison withsubblock affine motion compensation with minimal subblock size 4×4.Especially for content with fast rotation. For such content EIF can beused.

1.3 Enhanced Bilinear Interpolation Filter

Enhanced bi-linear Interpolation Filter (EIF) can be used for aprediction block and on subblock basis. The filtering procedure is thesame for luma and for chroma signals, the filtering procedure comprisesof following operations:

-   -   1. Deriving pixel-based motion vector field from the CPMVs,        according to the equation (1-1);    -   2. Obtaining interpolated samples based on the derived motion        vectors, using bilinear interpolation for the fractional        offsets;    -   3. Performing horizontal and then vertical filtering using fixed        3-tap high-pass filter [−1, 10, −1] with normalization factor of        8.

First two operations are performed for (w+2)×(h+2) area, where w and hare prediction block width and height correspondently; one pixel marginfrom each border is added for applying 3-tap filter at the third step.Original affine block and corresponding (w+2)×(h+2) block that is usedin intermediate step of EIF are depicted in FIG. 8 .

The example of EIF implementation is described below.

Interpolation process for the enhanced interpolation filter

Inputs to this process are:

-   -   a location (xCb, yCb) in full-sample units,    -   two variables cbWidth and cbHeight specifying the width and the        height of the current coding block,    -   horizontal change of motion vector dX,    -   vertical change of motion vector dY,    -   motion vector mvBaseScaled,    -   the selected reference picture sample arrays refPicLX,    -   sample bit depth bitDepth    -   width of the picture in samples pic_width,    -   height of the picture in samples pic_height,    -   clipMV flag specifying MV clipping type,    -   isLuma flag specifying whether luma or chroma is processed.

Outputs of this process are:

-   -   an (cbWidth/SubWidthC)×(cbHeight/SubHeightC) array predSamplesLX        of prediction sample values.

Interpolation filter coefficients T[p] for each fractional sampleposition p equal to xFrac or yFrac are specified in Table 8-16.

The variables hor_max, ver_max, hor_min and ver_min are derived byinvoking the process specified in 8.5.4.5 with a location (xCb, yCb) infull-sample units, two variables cbWidth and cbHeight specifying thewidth and the height of the current coding block, horizontal change ofmotion vector dX, vertical change of motion vector dY, motion vectormvBaseScaled, width of the picture in samples pic_width, height of thepicture in samples pic_height and clipMV flag as input, and hor_max,ver_max, hor_min and ver_min as output.

If isLuma is equal to FALSE, then variables mvBaseScaled, hor_min,hor_max, ver_min, ver_max are modified as follows:

xCb=xCb/SubWidthC  (8-748)

yCb=yCb/SubHeigthC  (8-749)

cbWidth=cbWidth/SubWidthC  (8-750)

cbHeight=cbHeight/SubHeightC  (8-751)

mvBaseScaled[0]=mvBaseScaled[0]/SubWidthC  (8-752)

mvBaseScaled[1]=mvBaseScaled[1]/SubHeightC  (8-753)

hor_min=hor_min/SubWidthC  (8-754)

hor_max=hor_max/SubWidthC  (8-755)

ver_min=ver_min/SubHeightC  (8-756)

ver_max=ver_max/SubHeightC  (8-757)

The variables shift0, shift1, offset0 and offset1 are derived asfollows:shift0 is set equal to bitDepth−8, offset0 is equal to 0,shift1 is set equal to 12−shift0, offset1 is equal to 2^(shift1−1) Forx=−1 . . . cbWidth and y=−1 . . . cbHeight, the following applies:

-   -   The motion vector mvX is derived as follows:

mvX[0]=(mvBaseScaled[0]+dX[0]*x+dY[0]*y)  (8-758)

mvX[1]=(mvBaseScaled[1]+dX[1]*x+dY[1]*y)  (8-759)

mvX[0]=Clip3(hor_min,hor_max,mvX[0])//a horizontal component of aclipped motion vector  (8-760)

mvX[1]=Clip3(ver_min,ver_max,mvX[1])/a vertical component of a clippedmotion vector  (8-761)

-   -   The variables xInt, yInt, xFrac and yFrac are derived as        follows:

x Int=xCb+(mvX[0]>>9)+x  (8-762)

y Int=yCb+(mvX[1]>>9)+y  (8-763)

xFrac=(mvX[0]>>4)& 31  (8-764)

yFrac=(mvX[1]>>4)& 31  (8-765)

-   -   The variables A and B are derived as follows:

A=(refPicLX[x Int][yInt]*T[xFrac][0]++refPicLX[xInt+1][yInt]*T[xFrac][1]+offset0)>>shift0  (8-766)

B=(refPicLX[x Int][yInt+1]*T[xFrac][0]++refPicLX[xInt+1][yInt+1]*T[xFrac][1]+offset0)>>shift0  (8-767)

-   -   The sample value b_(x,y) corresponding to location (x, y) is        derived as follows:

b _(x,y)=(A*T[yFrac][0]+B*T[yFrac][1]+offset1)>>shift1  (8-768)

The enhancement interpolation filter coefficients eF[ ] are specified as{−1, 10, −1}.

The variables shift2, shift3, offset2 and offset3 are derived asfollows:

-   -   shift2 is set equal to max(bit_depth−11, 0), offset2 is equal to        2^(shift2−1),    -   shift3 is set equal to (6−max(bit_depth−11, 0)), offset3 is        equal to 2^(shift3−1)        For x=0 . . . cbWidth−1 and y=−1 . . . cbHeight, the following        applies:

hxy=(eF[0]*b _(x−1,y) +eF[1]*b _(x,y) +eF[2]*b_(x+1,y)+offset2)>>shift2  (8-769)

For x=0 . . . cbWidth−1 and y=0 . . . cbHeight−1, the following applies:

-   -   predSamplesLX_(L)[x][y]=Clip3(0, (1<<bitDepth)−1,

(eF[0]*h _(x,y−1) +eF[1]*h _(x,y) +eF[2]*b_(x,y−1)+offset3)>>shift3)  (8-770)

TABLE 8-16 Specification of the interpolation filter coefficients T[p]for each fractional sample position p Fractional Interpolation filtersample coefficients position p T[p][0] T[p][1] 0 64 0 1 62 2 2 60 4 3 586 4 56 8 5 54 10 6 52 12 7 50 14 8 48 16 9 46 18 10 44 20 11 42 22 12 4024 13 38 26 14 36 28 15 34 30 16 32 32 17 30 34 18 28 36 19 26 38 20 2440 21 22 42 22 20 44 23 18 46 24 16 48 25 14 50 26 12 52 27 10 54 28 856 29 6 58 30 4 60 31 2 62

1.4 Adaptive Usage of EIF and Block-Based Affine Motion Compensation

EIF have less multiplications in comparison with subblock affine motioncompensation with minimal subblock sizes 8×8 and 4×4. However memorybandwidth for EIF without affine motion model restrictions can be huge.Also for effective hardware implementations of EIF some additionalrequirements can appears. For example, the following requirements canappears for EIF from the hardware perspective.

-   -   A. The internal buffer is limited by N lines, where N can be for        example 3, 4, 5 or more. This means that during processing of        one line (one row) of the current block (subblock) no more than        N lines from the reference picture can be used.    -   B. Memory access should be sequential, which means that if for        i_(th) line of current block j_(th) line of the reference        picture is fetched, then for (i+1)_(th) line of the current        block only lines j+1,j+2, . . . can be fetched.    -   C. No more than one additional line can be fetched for all lines        of the current block except for the first.

To combine benefits of 8×8 subblock based affine motion compensation andEIF, adaptive scheme of usage EIF and subblock affine motioncompensation.

1.4.1 Adaptive Usage of EIF and Block-Based Affine Motion Compensation.Basic Algorithm

Algorithm 1. Adaptive usage of EIF and block-based affine motioncompensation (basic algorithm)

The basic algorithm of adaptive usage of EIF and subblock affine motioncompensation is as follows.

-   -   1. Calculate optimal subblock size M×N based on affine motion        model parameters.    -   2. If both optimal subblock width M and optimal subblock height        N are greater or equal than 8, then perform subblock motion        compensation with M×N subblock.    -   3. Otherwise, check EIF applicability conditions        -   3.1. EIF applicability condition 1        -   3.2. EIF applicability condition 2        -   3.3 . . . .        -   3.4. EIF applicability condition P        -   3.5. If all EIF applicability conditions are met, then            perform EIF motion compensation.            -   EIF motion compensation process comprise:            -   3.5.1. Check EIF applicability condition P+1            -   3.5.2. Check EIF applicability condition P+2            -   3.5.3 . . . .            -   3.5.4. Check EIF applicability condition P+K            -   3.5.5. If one of EIF applicability conditions P+1 . . .                P+K are not met, then                -   3.5.5.1. calculate first motion vector range that                    provide fulfilment of conditions that were not met.                -   3.5.5.2. set second motion vector range equal to the                    first motion vector range            -   3.5.6. Otherwise                -   3.5.6.1. calculate third motion vector range                -   3.5.6.2. set second motion vector range equal to the                    third motion vector range            -   3.5.7. Clip motion vectors calculated according to                affine model to guarantee, that these vectors are in the                second motion vector range.        -   3.6. Otherwise set M=max(M, 8), N=max(N, 8) and perform            subblock motion compensation with M×N subblock.

In some embodiments P and K can be equal to zero that means that thealgorithm above may not have operations 3.1-3.4 if P is equal to zeroand may not have operations 3.5.1-3.5.4 if K is equal to zero.

The details of some operations of this basic algorithm is describedbelow.

1.4.1.1 Optimal Subblock Size Calculation

One method for deriving affine sub-block size is based on the motionvector differences of the affine control points and the width and heightof an affine block. The sub-block size M×N could be derived as byEquation (2-1), where MvPre is the motion vector accuracy (e.g., ¼ pelin HEVC standard or 1/16 pel in VVC and EVC standards), and affinemotion model parameters dHorX, dHorY, dVerX, dVerY are calculatedaccording to equations (1-4)-(1-7) for 6 parameter model and accordingto equations (1-8)-(1-11) for 4 parameter model.

$\begin{matrix}\left\{ \begin{matrix}{M = {{clip}3\left( {4,w,\frac{w \times {MvPre}}{\max\left( {{{abs}({dHorX})},{{abs}({dHorY})}} \right)}} \right)}} \\{N = {{clip}3\left( {4,h,\frac{h \times {MvPre}}{\max\left( {{{abs}({dVerX})},{{abs}({dVerY})}} \right)}} \right)}}\end{matrix} \right. & \left( {2 - 1} \right)\end{matrix}$

M and N derived in Equation (2-1) will be adjusted downward if necessaryto make sure that w and h is divisible by M and N, respectively.

Another method is to build a 3 dimensional looking up table, then getthe sub-block size directly from the looking up table according tomotion vector difference, block size, and motion vector precision. Forexample, set M to Table_M[x][y][z], where x equal to max(abs(v_(1x)−v_(0x)), abs(v_(1y)−v_(0y))), y equal to affine block width,z equal to the motion vector precision; set N to Table N[x][y][z], wherex equal to max (abs(v_(2x)−v_(0x)), abs(v_(2y)−v_(0y))), y equal toaffine block height, z equal to the motion vector precision.

In some embodiments operation 1 is implemented as follows:

1.4.1.1.1 Derivation Process for Affine Subblock Size

Inputs to this process are:

-   -   two variables cbWidth and cbHeight specifying the width and the        height of the luma coding block,    -   the number of control point motion vectors numCpMv,    -   the control point motion vectors cpMvLX[cpIdx], with cpIdx=0 . .        . numCpMv−1 and X being 0 or 1,    -   the prediction list utilization flags predFlagLX, with X being 0        or 1.

Outputs of this process are:

-   -   the size of luma coding subblocks in horizontal direction        sizeSbX and in vertical direction sizeSbY,

sizeSbX is set equal to cbWidth, sizeSbY is set equal to cbHeight.

When predFlagLX is equal to 1, the following applies for X being 0 and1:

-   -   Horizontal change of motion vector dX, vertical change of motion        vector dY and base motion vector mvBaseScaled are derived by        invoking the process specified in clause 1.4.1.1.2 with the luma        coding block width cbWidth, the luma coding block height        cbHeight, number of control point motion vectors numCpMv and the        control point motion vectors cpMvLX[cpIdx] with cpIdx=0 . . .        numCpMv−1 as inputs.    -   The variable mvWx and mvWy are derived as follows:        -   mvWx=max(abs(dX[0]), abs(dX[1]))        -   mvWy=max(abs(dY[0]), abs(dY[1]))    -   The variable sizeSbXTemp is specificed in Table 8-5 according to        the value of mvWx.    -   The variable sizeSbYTemp is specificed in Table 8-5 according to        the value of mvWy.    -   The variable sizeSbX is modified as follow:        -   sizeSbX=min(sizeSbX, sizeSbXTemp)    -   The variable sizeSbY is modified as follow:        -   sizeSbY=min(sizeSbY, sizeSbYTemp)

TABLE 8-5 Specification of sizeSbXTemp for various input values of mvWxmvWx 0 1 2 3 4 >4 sizeSbX cb Width 32 16 8 8 4

TABLE 8-5 Specification of sizeSbYTemp for various input values of mvWymvWx 0 1 2 3 4 >4 size Sb Y cbHeight 32 16 8 8 4

Where clause 1.4.1.1.2 is described as follows:

1.4.1.1.2 Derivation Process for Affine Motion Model Parameters fromControl Point Motion Vectors

Inputs to this process are:

-   -   two variables cbWidth and cbHeight specifying the width and the        height of the luma coding block,    -   the number of control point motion vectors numCpMv,    -   the control point motion vectors cpMvLX[cpIdx], with cpIdx=0 . .        . numCpMv−1 and X being 0 or 1.

Outputs of this process are:

-   -   horizontal change of motion vector dX,    -   vertical change of motion vector dY,    -   motion vector mvBaseScaled corresponding to the top left corner        of the luma coding block.

The variables log 2 CbW and log 2 CbH are derived as follows:

log 2CbW=Log 2(cbWidth)  (8-688)

log 2CbH=Log 2(cbHeight)  (8-689)

Horizontal change of motion vector dX is derived as follows:

dX[0]=(cpMvLX[1][0]−cpMvLX[0][0])<<(7−log 2CbW)  (8-690)

dX[1]=(cpMvLX[1][1]−cpMvLX[0][1])<<(7−log 2CbW)  (8-691)

Vertical change of motion vector dY is derived as follows:

-   -   If numCpMv is equal to 3, dY is derived as follow:

dY[0]=(cpMvLX[2][0]−cpMvLX[0][0])<<(7−log 2CbH)  (8-692)

dY[1]=(cpMvLX[2][1]−cpMvLX[0][1])<<(7−log 2CbH)  (8-693)

-   -   Otherwise (numCpMv is equal to 2), dY is derived as follows:

dY[0]=−dX[1]  (8-694)

dY[1]=dX[0]  (8-695)

Motion vector mvBaseScaled corresponding to the top left corner of theluma coding block is derived as follows:

mvBaseScaled[0]=cpMvLX[0][0]<<7  (8-696)

mvBaseScaled[1]=cpMvLX[0][1]<<7  (8-697)

1.4.1.2 EIF Applicability Conditions

EIF applicability conditions can be for example as following

-   -   1. Memory bandwidth restrictions. This kind of restrictions        guarantee that the size of area in the reference picture        corresponding to the current affine block (EIF block) is no more        than predefined threshold T. The example of definition of area        in the reference picture corresponding to the current affine        block is depicted in FIG. 9 .    -   2. The internal buffer is limited by R lines, where R is        predefined value and can be for example 3, 4, 5 or more. This        means that during processing of one line (one row) of the        current block (subblock) no more than R lines from the reference        picture can be used.    -   3. Memory access should be sequential, which means that if for        i_(th) line of current block j_(th) line of the reference        picture is fetched, then for (i+1)_(th) line of the current        block only lines j+1, j+2, . . . can be fetched.    -   4. No more than one additional line can be fetched for all lines        of the current block except for the first.    -   5. The inequalities for affine motion model parameters, for        example as following

$\begin{matrix}\left\{ {\begin{matrix}{a \leq {dHorX} \leq b} \\{c \leq {dHorY} \leq d} \\{e \leq {dVerX} \leq f} \\{g \leq {dVerY} \leq h}\end{matrix},} \right. & {a.}\end{matrix}$

where a, b, c, d, e, f, g, h are predefined values or plus/minusinfinity.

$\begin{matrix}\left\{ {\begin{matrix}{{dHorX} \leq {a*{dVerX}}} \\{{dVerY} \leq {b*{dHorY}}}\end{matrix},} \right. & {b.}\end{matrix}$

where a and b are predefined values

In one example with specific EIF applicability conditions, basicalgorithm is as follows:

Algorithm 2. Adaptive Usage of EIF and Block-Based Affine MotionCompensation with Specific EIF Applicability Conditions

-   -   1. Calculate optimal subblock size M×N based on affine motion        model parameters.    -   2. If both optimal subblock width M or optimal subblock height N        is greater or equal than 8, then perform subblock motion        compensation with M×N subblock.    -   3. Otherwise, check EIF applicability conditions:        -   3.1. EIF applicability condition 1: The internal buffer is            limited by R lines, where R is predefined value and can be            for example 3, 4, 5 or more. This means that during            processing of one line (one row) of the current block            (subblock) no more than R lines from the reference picture            can be used.        -   3.2. EIF applicability condition 2: Memory access should be            sequential, which means that if for i_(th) line of current            block j_(th) line of the reference picture is fetched, then            for (i+1)th line of the current block only lines j+1, j+2, .            . . can be fetched.        -   3.3. EIF applicability condition 3: No more than one            additional line can be fetched for all lines of the current            block except for the first.        -   3.4 . . . .        -   3.5. EIF applicability condition P        -   3.6. If all EIF applicability conditions are met, then            perform EIF motion compensation. EIF motion compensation            process comprise:            -   3.6.1. Check EIF applicability condition P+1: Checking                memory bandwidth restrictions. This kind of restrictions                guarantee that the size of area in the reference picture                corresponding to the current affine block (EIF block) is                no more than predefined threshold T. The example of                definition of area in the reference picture                corresponding to the current affine block is depicted in                FIG. 9 .            -   3.6.2 . . . .            -   3.6.3. Check EIF applicability condition P+K            -   3.6.4. If one of EIF applicability conditions P+1 . . .                P+K are not met, then                -   3.6.4.1. calculate first motion vector range that                    provide fulfilment of conditions that were not met.                -   3.6.4.2. set second motion vector range equal to the                    first motion vector range            -   3.6.5. Otherwise                -   3.6.5.1. calculate third motion vector range                -   3.6.5.2. set second motion vector range equal to the                    third motion vector range            -   3.6.6. Clip motion vectors calculated according to                affine model to guarantee, that these vectors are in the                second motion vector range.    -   3.7. Otherwise set M=max(M, 8), N=max(N, 8) and perform subblock        motion compensation with M×N subblock.

In one embodiment operations 3.1-3.5 are implemented as follows:

When predFlagLX is equal to 1, the following applies for X being 0 and1:

-   -   Horizontal change of motion vector dX, vertical change of motion        vector dY and base motion vector mvBaseScaled are derived by        invoking the process specified in clause 1.4.1.1.2 with the luma        coding block width cbWidth, the luma coding block height        cbHeight, number of control point motion vectors numCpMv and the        control point motion vectors cpMvLX[cpIdx] with cpIdx=0 . . .        numCpMv−1 as inputs.

If dY[1] is less than ((−1)<<9), then the variable eifCanBeAppliedX isequal to FALSE

-   -   Otherwise,        -   If (max(0, dY[1])+Abs(dX[1]))*(1+eifSubblockSize) is greater            than (1<<9) then the variable eifCanBeAppliedX is equal to            FALSE.

The variable eifCanBeAppliedX equal to TRUE here means that all EIFapplicability conditions 1−P (operations 3.1-3.5 of algorithm 2) aremet.

The details about operation 3.6.1 of the algorithm 2 are provided below.

1.4.1.2.1 Memory Access Consumption Calculation for Affine Block in Caseof Usage EIF (Operation 3.6.1 of Algorithm 2)

The following operations are performed for memory access consumptioncalculation:

-   -   1. Derive the location of each corner sample of the W×H        subblock.    -   2. Derive the location of each corner sample of the subblock        used on operation 3 of EIF (denote it as EIF intermediate        subblock).    -   3. Derive motion vectors for each corner sample of EIF        intermediate subblock.    -   4. Derive location of transformed subblock in reference picture.    -   5. Derive the bounding box size for the transformed subblock.    -   6. Get the memory access consumption based on the bounding box        size for transformed subblock size and filter length (EIF uses        bilinear interpolation, so filter length is equal to 2).

The details of implementation of these operations are described below.

Operation 1. Derive the Location of Each Corner Sample of the AffineSubblock

Denote (x0, y0) as the coordinate of the top-left sample of the affineblock. In this embodiment for memory access consumption calculation, itis supposed that coordinate of the top-left sample of the affine blockis equal to (1, 1). The position (x₀, y₀) does not make sense for memoryaccess consumption calculation and with (x₀, y₀)=(1, 1) the equationsare simpler. Then the location of the affine block can be descripted bythe coordinates of its corner samples (top-left, top-right, bottom-left,bottom-right):

$\begin{matrix}\left\{ \begin{matrix}{\left( {x_{0},y_{0}} \right) = \left( {1,1} \right)} \\{\left( {x_{1},y_{1}} \right) = \left( {W,1} \right)} \\{\left( {x_{2},y_{2}} \right) = \left( {1,H} \right)} \\{\left( {x_{3},y_{3}} \right) = \left( {W,H} \right)}\end{matrix} \right. & \left( {3 - 1} \right)\end{matrix}$

Operation 2. Derive the Location of Each Corner Sample of the EIFIntermediate Subblock

Due to EIF uses 3-tap filter at the operation 3, bilinear interpolationat the operation 2 of EIF is performed for (W+2)×(H+2) subblock (onepixel margin from each border is added). This (W+2)×(H+2) subblock isdenoted as intermediate EIF subblock. The coordinates of intermediateEIF block corner samples (top-left, top-right, bottom-left,bottom-right) are:

$\begin{matrix}\left\{ \begin{matrix}{\left( {X_{0},Y_{0}} \right) = \left( {0,0} \right)} \\{\left( {X_{1},Y_{1}} \right) = \left( {{1 + W},0} \right)} \\{\left( {X_{2},Y_{2}} \right) = \left( {0,{1 + H}} \right)} \\{\left( {X_{3},Y_{3}} \right) = \left( {{1 + W},{1 + H}} \right)}\end{matrix} \right. & \left( {3 - 2} \right)\end{matrix}$

The coordinates of corners of affine subblock and of intermediate EIFsubblock are depicted in FIG. 8 .

Operation 3. Derive Motion Vectors for Each Corner Sample of EIFIntermediate Subblock

The initial motion vector (mv_(0x), mv_(0y)) does not make sense formemory access consumption calculation and with (mv_(0x),mv_(0y))=(dHorX+dVerX, dHorY+dVerY) the equations are simpler.

Motion vectors are derived according to equation (1-1).

$\begin{matrix}\left\{ \begin{matrix}{{V_{0}V_{X_{0},Y_{0}}} = \left( {0,0} \right)} \\{V_{1} = {V_{X_{1},Y_{1}} = \left( {{\left( {W + 1} \right){dHorX}},{\left( {W + 1} \right){dHorY}}} \right)}} \\{V_{2} = {V_{X_{2},Y_{2}} = \left( {{\left( {H + 1} \right){dVerX}},{\left( {H + 1} \right){dVerY}}} \right)}} \\{V_{3} = {V_{X_{3},Y_{3}} = \left( {{{\left( {W + 1} \right){dHorX}} + {\left( {H + 1} \right){dVerX}}},{{\left( {W + 1} \right){dHorY}} + {\left( {H + 1} \right){dVerY}}}} \right)}}\end{matrix} \right. & \left( {3 - 3} \right)\end{matrix}$

Operation 4. Derive Location of Transformed Block in Reference Picture

The location of the transformed block in reference picture can bedescripted by the coordinates of its corner samples (top-left,top-right, bottom-left, bottom-right):

$\begin{matrix}\left\{ \begin{matrix}{\left( {X_{0}^{\prime},Y_{0}^{\prime}} \right) = \left( {0,0} \right)} \\{\left( {X_{1}^{\prime},Y_{1}^{\prime}} \right) = \left( {{1 + W + {\left( {W + 1} \right){dHorX}}},{\left( {W + 1} \right){dHorY}}} \right)} \\{\left( {X_{2}^{\prime},Y_{2}^{\prime}} \right) = \left( {{\left( {H + 1} \right){dVerX}},{1 + H + {\left( {H + 1} \right){dVerY}}}} \right)} \\{\left( {X_{3}^{\prime},Y_{3}^{\prime}} \right) = \left( {{1 + W + {\left( {W + 1} \right){dHorX}} + {\left( {H + 1} \right){dVerX}}},{1 + H + {\left( {W + 1} \right){dHorY}} + {\left( {H + 1} \right){dVerY}}}} \right)}\end{matrix} \right. & \left( {3 - 4} \right)\end{matrix}$

Operation 5. Derive the Bounding Box Size for the Transformed Subblock

The bounding box size for transformed subblock in reference picture canbe calculated by following equation, where max function returns themaximum value of the arguments, min function returns the minimum valueof the arguments:

$\begin{matrix}\left\{ \begin{matrix}{W^{\prime} = {{\max\left( {X_{0}^{\prime},X_{1}^{\prime},X_{2}^{\prime},X_{3}^{\prime}} \right)} - {\min\left( {X_{0}^{\prime},X_{1}^{\prime},X_{2}^{\prime},X_{3}^{\prime}} \right)} + 1}} \\{H^{\prime} = {{\max\left( {Y_{0}^{\prime},Y_{1}^{\prime},Y_{2}^{\prime},Y_{3}^{\prime}} \right)} - {\min\left( {Y_{0}^{\prime},Y_{1}^{\prime},Y_{2}^{\prime},Y_{3}^{\prime}} \right)} + 1}}\end{matrix} \right. & \left( {3 - 5} \right)\end{matrix}$

The location of transformed subblock in reference picture andcorresponding bounding box are depicted in FIG. 9 .

In one example W′=Ceil(W′), H′=Ceil(H′) is performed after equation(3-5).

In another example W′=Floor(W′), H′=Floor(H′) is performed afterequation (3-5).

Operation 6. Get the Memory Access Consumption

The memory access consumption of the affine subblock in one referencepicture can be decided, by the bounding box size for the transformedsubblock size and the length of MC interpolation filter for affinemotion block T′, e.g., 2, 4, 6, 8 . . . . :

Mem=(W′+T′−1)*(H′+T′−1)  (3-6)

For EIF, bilinear interpolation is used, therefore filter length is 2and memory access consumption is equal to

Mem=(W′+1)*(H′+1)  (3-7)

1.4.1.2.2 Affine Motion Model Restrictions for EIF (Operation 3.6.1 ofAlgorithm 2)

Denote target worst case memory bandwidth as

${T = \frac{S_{wc}}{W*H}},$

where W and H are current subblock width and heights respectively, andS_(wc) is maximum allowed memory access consumption for the currentsubblock, according to the target case memory bandwidth. To guaranteethat EIF memory bandwidth is not greater that the target case memorybandwidth, the memory access consumption of EIF subblock should beconstrained as following condition:

$\begin{matrix}{{\frac{\left( {W^{\prime} + 1} \right)*\left( {H^{\prime} + 1} \right)}{W*H} \leq T}{or}{{\left( {W^{\prime} + 1} \right)*\left( {H^{\prime} + 1} \right)} \leq {T*W*H}}{or}{{\left( {W^{\prime} + 1} \right)*\left( {H^{\prime} + 1} \right)} \leq S_{wc}}} & \left( {3 - 8} \right)\end{matrix}$

The value T can be predefined in both encoder and decoder, or specifiedin a parameter set of a codec video sequence, e.g., sequence levels,picture level, slice level parameter set, etc.

In one example, if the maximum allowed memory access consumption persample is defined as the memory access consumption of a 4×4 block, thenT can be derived as follows, where T is the length of interpolationfilter:

$\begin{matrix}{T = \frac{\left( {4 + T^{\prime} - 1} \right)*\left( {4 + T^{\prime} - 1} \right)}{4*4}} & \left( {3 - 9} \right)\end{matrix}$

For T′ equal to 6 the restriction is as follows:

(W′+1)*(H′+1)≤(4+6−1)*(4+6−1)  (3-10)

In another example, if the maximum allowed memory access consumption persample is defined as the memory access consumption of a 8×8 block, thenT can be derived as follows, where T is the length of interpolationfilter:

$\begin{matrix}{T = \frac{\left( {8 + T^{\prime} - 1} \right)*\left( {8 + T^{\prime} - 1} \right)}{8*8}} & \left( {3 - 11} \right)\end{matrix}$

In another example, the maximum allowed memory access consumption of persample can be different according the prediction direction of currentblock, i.e.: when current block is uni-prediction, use thresholdT_(UNI), when current block is bi-prediction, use threshold T_(BI).

For example, T_(UNI) is defined as the memory access consumption of 4×4block, T_(BI) is defined as the memory access consumption of 8×4 block,then:

$\begin{matrix}{T_{UNI} = \frac{\left( {4 + T^{\prime} - 1} \right)*\left( {4 + T^{\prime} - 1} \right)}{4*4}} & \left( {3 - 12} \right)\end{matrix}$ $\begin{matrix}{T_{Bi} = \frac{\left( {8 + T^{\prime} - 1} \right)*\left( {4 + T^{\prime} - 1} \right)}{8*4}} & \left( {3 - 13} \right)\end{matrix}$

In another example, T_(UNI) is defined as the memory access consumptionof 4×4 block, T_(BI) is defined as the memory access consumption of 8×8block, then:

$\begin{matrix}{T_{UNI} = \frac{\left( {4 + T^{\prime} - 1} \right)*\left( {4 + T^{\prime} - 1} \right)}{4*4}} & \left( {3 - 14} \right)\end{matrix}$ $\begin{matrix}{T_{Bi} = \frac{\left( {8 + T^{\prime} - 1} \right)*\left( {8 + T^{\prime} - 1} \right)}{8*8}} & \left( {3 - 15} \right)\end{matrix}$

T′ in the examples above is the length of motion compensation (MC)interpolation filter for translational motion block, e.g., 2, 4, 6, 8 .. . .

The value of T, T_(UNI) and T_(BI) may depend on width and height of thecurrent block.

For bi-prediction affine block, the above constraint is applied to bothlist0 and list1, individually.

In another example memory access consumption is calculated for list0 andfor list1 as Mem₀ and Mem₁ and sum of these elements is restricted. Forexample if the T_(BI) is defined as the memory access consumption of 8×8block the following restriction is used:

Mem₀+Mem₁≤2*(8+T′−1)*(8+T′−1)  (3-16)

If the condition (3-8) is not met, the motion vector range thatguarantee required size of the bounding box is derived and during MVcalculation in EIF according to equation (1-1), the horizontal andvertical parts of motion vectors are clipped according to the derivedrange. The motion vector range derivation is described in section1.4.1.2.3.

Operation 3.6.1 of the algorithm 2 can be implemented as follows:

The variable clipMVX is derived as follows for X being 0 and 1:

-   -   clipMVX is set equal to FALSE

The variable eifSubblockSize is set equal to 4.

When predFlagLX is equal to 1, the following applies for X being 0 and1:

-   -   Horizontal change of motion vector dX, vertical change of motion        vector dY and base motion vector mvBaseScaled are derived by        invoking the process specified in clause 1.4.1.1.2 with the luma        coding block width cbWidth, the luma coding block height        cbHeight, number of control point motion vectors numCpMv and the        control point motion vectors cpMvLX[cpIdx] with cpIdx=0 . . .        numCpMv−1 as inputs.    -   The variable mvWx and mvWy are derived as follows:        -   mvWx=max(abs(dX[0]), abs(dX[1]))        -   mvWy=max(abs(dY[0]), abs(dY[1]))    -   The variable sizeSbXTemp is specificed in Table 8-5 according to        the value of mvWx.    -   The variable sizeSbYTemp is specificed in Table 8-5 according to        the value of mvWy.    -   The variable sizeSbX is modified as follow:        -   sizeSbX=min(sizeSbX, sizeSbXTemp)    -   The variable sizeSbY is modified as follow:        -   sizeSbY=min(sizeSbY, sizeSbYTemp)

TABLE 8-5 Specification of sizeSbXTemp for various input values of mvWxmvWx 0 1 2 3 4 >4 sizeSbX cb Width 32 16 8 8 4

TABLE 8-5 Specification of sizeSbYTemp for various input values of mvWymvWx 0 1 2 3 4 >4 size Sb Y cbHeight 32 16 8 8 4

-   -   The variable clipMVX are modified as follows:        -   The arrays X[i], Y[i] are derived as follows:            -   X[0]=0            -   X[1]=(eifSubblockSize+1)*(dX[0]+(1<<9))            -   X[2]=(eifSubblockSize+1)*dY[0]            -   X[3]=X[1]+X[2]            -   Y[0]=0            -   Y[1]=(eifSubblockSize+1)*dX[1]            -   Y[2]=(eifSubblockSize+1)*(dY[1]+(1<<9))            -   Y[3]=Y[1]+Y[2]            -   The variable Xmax is set equal to maximum of X[i] for i                is equal 0 . . . 3            -   The variable Xmin is set equal to minimum of X[i] for i                is equal 0 . . . 3            -   The variable Ymax is set equal to maximum of Y[i] for i                is equal 0 . . . 3            -   The variable Ymin is set equal to minimum of Y[i] for i                is equal 0 . . . 3            -   The variable W is set equal to (Xmax−Xmin+(1<<9)−1)>>9            -   The variable H is set equal to (Ymax−Ymin+(1<<9)−1)>>9            -   If (W+2)*(H+2) is greater than 81, the variable clipMVX                is set equal to TRUE

The variables eifCanBeApplied and clipMV are derived as following:

-   -   clipMV=clipMV0|clipMV1

The variable clipMV equal to TRUE here means that memory bandwidth EIFapplicability condition is not met and further my clipping is needed(operations 3.6.4-3.6.6 of the Algorithm 2)

The section below describes the conventional method of the motion vectorrange updating near the picture boundaries. The examples of applying theconventional method are depicted in FIG. 10-14 at the left part (underthe title “Conventional design”).

1.4.1.2.3 Derivation of Clipping Parameters for Affine Motion Vector(Operations 3.6.4-3.6.5 of the Algorithm 2)

Inputs to this process are:

-   -   a location (xCb, yCb) in full-sample units,    -   two variables cbWidth and cbHeight specifying the width and the        height of the current coding block,    -   horizontal change of motion vector dX,    -   vertical change of motion vector dY,    -   motion vector mvBaseScaled,    -   width of the picture in samples pic_width,    -   height of the picture in samples pic_height,    -   clipMV flag specifying if MV clipping is to be applied (this        flag specify whether EIF memory access conditions are fulfilled        or not)

Outputs of this process are:

-   -   hor_max, ver_max, hor_min and ver_min that denotes the maximum        and minimum allowed motion vector horizontal and vertical        components.

The center motion vector mv_center is derived as follows:

mv_center[0]=(mvBaseScaled[0]+dX[0]*(cbWidth>>1)+dY[0]*(cbHeight>>1))  (8-743)

mv_center[1]=(mvBaseScaled[1]+dX[1]*(cbWidth>>1)+dY[1]*(cbHeight>>1))  (8-743)

The rounding process for motion vectors as specified in clause 8.5.3.10is invoked with mv_center, rightShift set equal to 5, and leftShift setequal to 0 as inputs and the rounded motion vector is return asmv_center.

The motion vector mv_center is clipped as follows:

mv_center[0]=Clip3(−2¹⁷,2¹⁷−1,mv_center[0])  (8-686)

mv_center[1]=Clip3(−2¹⁷,2¹⁷−1,mv_center[1])  (8-686)

The variables hor_max_pic, ver_max_pic, hor_min_pic and ver_min_pic arederived as follows:

hor_max_pic=(pic_width+128−xCb−cbWidth)<<4  (8-743)

ver_max_pic=(pic_height+128−yCb−cbHeight)<<4  (8-743)

hor_min_pic=(−128−xCb)<<4  (8-743)

ver_min_pic=(−128−yCb)<<4  (8-743)

If clipMV is equal to FALSE, then the output variables hor_max, ver_max,hor_min and ver_min that denotes the maximum and minimum allowed motionvector horizontal and vertical components are derived as following (thiscorresponds to operation 3.6.5 of the algorithm 2):

hor_max=hor_max_pic<<5  (8-743)

ver_max=ver_max_pic<<5  (8-743)

hor_min=hor_min_pic<<5  (8-743)

ver_min=ver_min_pic,<<5  (8-743)

Otherwise if clipMV is equal to TRUE, the following operations areapplied (this corresponds to operation 3.6.4 of the algorithm 2):

-   -   The variables mv_hor_min, mv_ver_min, mv_hor_max and mv_ver_max        are derived as following:

mv_hor_min=mv_center[0]−deviationMV [log 2CbWidth−3]  (8-743)

mv_ver_min=mv_center[1]−deviationMV[log 2CbHeight−3]  (8-743)

mv_hor_max=mv_center[0]+deviationMV[log 2CbWidth−3]  (8-743)

mv_ver_max=mv_center[1]+deviationMV [log 2CbHeight−3]  (8-743)

-   -   with array deviationMV specified for k=0 . . . 4 as        deviationMV[k]={64, 128, 272, 560, 1136}.    -   The variables hor_max, ver_max, hor_min and ver_min are derived        as following:

mv_hor_max=max(mv_hor_max,hor_min)  (8-743)

mv_ver_max=max(mv_ver_max,ver_min)  (8-743)

mv_hor_min=min(mv_hor_min,hor_max)  (8-743)

mv_ver_min=min(mv_ver_min,ver_max)  (8-743)

hor_max=min(hor_max_pic,mv_hor_max)<<5  (8-743)

ver_max=min(ver_max_pic,mv_ver_max)<<5  (8-743)

hor_min=max(hor_min_pic,mv_hor_min)<<5  (8-743)

ver_min=max(ver_min_pic,mv_ver_min)<<5  (8-743)

2 Problems of the Conventional Design

The conventional design of MV clipping parameters derivation has thefollowing problems:

-   -   1. Motion vector range is significantly reduced if central        motion vector is close to the picture boundaries

For example if central motion vector points outside the pictureboundary, the motion vector range shrinks significantly as depicted inFIG. 10, 11 . In some corner cases motion vector range can even collapseto the one point as depicted in FIG. 14 . Motion vector range reductioncause to motion model degradation. So, instead of the real motion field(“true motion”) (e.g. affine motion like rotation or zooming) predictionsignal is generated based on the motion field corrupted by clippings tothe small motion vector range. This in turn causes to prediction signalquality degradation, which results to bitrate increasing (due to morebits is needed to the residual signal coding) or reconstruction signalquality degradation.

3 Detailed Description 3.1 Motion Vector Range Derivation Near thePicture Boundaries

In conventional design of MV clipping range derivation for EIF, MV rangeis significantly reduced in case of central MV, calculated in section1.4.1.2.3, is close to the picture boundary or outside of the pictureboundary. For example, for horizontal direction, if MV spread is greaterthan the distance from (x₀+mv_center[0]) to the left picture boundary,motion vector range will be reduced as depicted in FIG. 12 . If(x₀+mv_center[0]) refer to the position outside the picture boundary(e.g. x₀+mv_center[0]<0 or x₀+mv_center[0]<−MAX_CU_SIZE in someembodiments) the MV range will be reduced to only one point as depictedin FIG. 13 . The picture for the right picture boundary is symmetric.

To avoid reducing MV range in described specific cases the followingsolution is proposed. In case of MV range, calculated based on centralmotion vector (mv_center), comprise MVs pointing outside the pictureboundary (outside the picture boundary with MAX_CU_SIZE margin in someembodiments) MV range is calculated based on picture boundary instead ofcentral motion vector. The examples of using new design are depicted inFIG. 12 and FIG. 13 . The example embodiment of MV range calculation(section 1.4.1.2.3) is described below.

Derivation of Clipping Parameters for Affine Motion Vector (Embodiment1)

Inputs to this process are:

-   -   a location (xCb, yCb) in full-sample units,    -   two variables cbWidth and cbHeight specifying the width and the        height of the current coding block,    -   horizontal change of motion vector dX,    -   vertical change of motion vector dY,    -   motion vector mvBaseScaled,    -   width of the picture in samples pic_width,    -   height of the picture in samples pic_height,    -   clipMV flag specifying MV clipping type.

Outputs of this process are:

-   -   hor_max, ver_max, hor_min and ver_min that denotes the maximum        and minimum allowed motion vector horizontal and vertical        components.

The variables log 2 CbW and log 2 CbH are derived as follows:

log 2CbWidth=Log 2(cbWidth)  (8-774)

log 2CbHeight=Log 2(cbHeight)  (8-775)

The variables hor_max_pic, ver_max_pic, hor_min_pic and ver_min_pic arederived as follows:

hor_max_pic=(pic_width+128−xCb−cbWidth−1)<<5  (8-776)

ver_max_pic=(pic_height+128−yCb−cbHeight−1)<<5  (8-777)

hor_min_pic=(−128−xCb)<<5  (8-778)

ver_min_pic=(−128−yCb)<<5  (8-779)

The variables hor_max_pic, ver_max_pic, hor_min_pic and ver_min_picrepresent the second motion vector range that is used to check whether amotion vector points inside the “first area including referencepicture”.

The center motion vector mv_center is derived as follows:

mv_center[0]=(mvBaseScaled[0]+dX[0]*(cbWidth>>1)+dY[0]*(cbHeight>>1))  (8-780)

mv_center[1]=(mvBaseScaled[1]+dX[1]*(cbWidth>>1)+dY[1]*(cbHeight>>1))  (8-781)

An operation of “obtaining a center motion vector, mv_center of a codingblock” in the present disclosure corresponds to the equations (8-780)and (8-781).

The rounding process for motion vectors as specified in clause 8.5.3.10is invoked with mv_center, rightShift set equal to 4, and leftShift setequal to 0 as inputs and the rounded motion vector is return asmv_center.

If clipMV is equal to FALSE, then the output variables hor_max, ver_max,hor_min and ver_min that denotes the maximum and minimum allowed motionvector horizontal and vertical components are set equal to variableshor_max_pic, ver_max_pic, hor_min_pic and ver_min_pic respectively.

Otherwise, the following operations are applied:

-   -   The array deviationMV is set equal to {128, 256, 544, 1120,        2272}.    -   The variables mv_hor_min, mv_ver_min, mv_hor_max and mv_ver_max        (hor_min, ver_min, hor_max and ver_max, used in the below) are        derived as following:

hor_min=mv_center[0]−deviationMV[log 2CbWidth−3]  (8-788)

ver_min=mv_center[1]−deviationMV[log 2CbHeight−3]  (8-789)

hor_max=mv_center[0]+deviationMV[log 2CbWidth−3]  (8-790)

ver_max=mv_center[1]+deviationMV[log 2CbHeight−3]  (8-791)

An operation of “deriving a first motion vector range for the codingblock based on the center motion vector and a motion vector spread,wherein the motion vector spread depends on a size of the coding block”in the present disclosure corresponds to the equations (8-788)-(8-791).Motion vector spread is represented by a horizontal motion vector spreaddeviationMV[log 2 CbHeight−3] and a vertical motion vector spread [log 2CbHeight−3].

-   -   If hor_min is less than hor_min_pic, the variables hor_min and        hor_max are updated as following:

hor_min=hor_min_pic  (8-792)

hor_max=min(hor_max_pic,hor_min_pic+2*deviationMV[log2CbWidth−3])  (8-793)

-   -   Otherwise, if hor_max is greater than hor_max_pic, the variables        hor_min and hor_max are updated as following:

hor_min=max(hor_min_pic,hor_max_pic−2*deviationMV[log2CbWidth−3])  (8-794)

hor_max=hor_max_pic  (8-795)

-   -   If ver_min is less than ver_min_pic, the variables ver_min and        ver_max are updated as following:

ver_min=ver_min_pic  (8-796)

ver_max=min(ver_max_pic,ver_min_pic+2*deviationMV[log2CbHeight−3])  (8-797)

-   -   Otherwise, if ver_max is greater than ver_max_pic, the variables        ver_min and ver_max are updated as following:

ver_min=max(ver_min_pic,ver_max_pic−2*deviationMV[log2CbHeight−3])  (8-798)

ver_max=ver_max_pic  (8-799)

An operation of “if the first motion vector range is at least partiallypointing outside a first area including a reference picture, updatingthe first motion vector range to be pointing within the first area” inthe present disclosure corresponds to the equations (8-792)-(8-799) andthe corresponding conditions above.

The output variables hor_max, ver_max, hor_min and ver_min are clippedas follows:

hor_max=Clip3(−2¹⁷,2¹⁷−1,hor_max)  (8-800)

ver_max=Clip3(−2¹⁷,2¹⁷−1,ver_max)  (8-801)

hor_min=Clip3(−2¹⁷,2¹⁷−1,hor_min)  (8-802)

ver_min=Clip3(−2¹⁷,2¹⁷−1,ver_min)  (8-803)

An operation of “performing a clipping operation on the updated firstmotion vector range to be within the range [−2¹⁷, 2¹⁷−1]” in the presentdisclosure corresponds to the equations (8-800)-(8-803).

It can be noted that the second motion vector range is represented byhor_max_pic, ver_max_pic, hor_min_pic and ver_min_pic in equations(8-776) to (8-779).

It can be noted that the first motion vector range is represented byhor_min, ver_min, hor_max and ver_max in equations (8-788) to (8-791).

It can be noted that the updated first motion vector range isrepresented by hor_min, ver_min, hor_max and ver_max in equations(8-792) to (8-799).

It can be noted that the variables hor_min, ver_min, hor_max and ver_maxlocated as right in equations (8-800) to (8-803) representingcorrespondingly the first minimum MV horizontal component value, thefirst minimum MV vertical component value, the first maximum MVhorizontal component value and the first maximum MV vertical componentvalue of the updated first motion vector range.

It can be noted that the variables hor_min, ver_min, hor_max and ver_maxlocated as left in equations (8-800) to (8-803) representingcorrespondingly the first minimum MV horizontal component value, thefirst minimum MV vertical component value, the first maximum MVhorizontal component value and the first maximum MV vertical componentvalue of the updated and clipped first motion vector range.

Derivation of clipping parameters for affine motion vector (embodiment2)

Inputs to this process are:

-   -   a location (xCb, yCb) in full-sample units,    -   two variables cbWidth and cbHeight specifying the width and the        height of the current coding block,    -   horizontal change of motion vector dX,    -   vertical change of motion vector dY,    -   motion vector mvBaseScaled,    -   width of the picture in samples pic_width,    -   height of the picture in samples pic_height,    -   clipMV flag specifying MV clipping type.

Outputs of this process are:

-   -   hor_max, ver_max, hor_min and ver_min that denotes the maximum        and minimum allowed motion vector horizontal and vertical        components.

The variables log 2 CbW and log 2 CbH are derived as follows:

log 2CbWidth=Log 2(cbWidth)  (8-774)

log 2CbHeight=Log 2(cbHeight)  (8-775)

The variables hor_max_pic, ver_max_pic, hor_min_pic and ver_min_pic arederived as follows:

hor_max_pic=(pic_width−xCb−cbWidth−1)<<5  (8-776)

ver_max_pic=(pic_height−yCb−cbHeight−1)<<5  (8-777)

hor_min_pic=(−xCb)<<5  (8-778)

ver_min_pic=(−yCb)<<5  (8-779)

The center motion vector mv_center is derived as follows:

mv_center[0]=(mvBaseScaled[0]+dX[0]*(cbWidth>>1)+dY[0]*(cbHeight>>1))  (8-780)

mv_center[1]=(mvBaseScaled[1]+dX[1]*(cbWidth>>1)+dY[1]*(cbHeight>>1))  (8-781)

The rounding process for motion vectors as specified in clause 8.5.3.10is invoked with mv_center, rightShift set equal to 4, and leftShift setequal to 0 as inputs and the rounded motion vector is return asmv_center.

If clipMV is equal to FALSE, then the output variables hor_max, ver_max,hor_min and ver_min that denotes the maximum and minimum allowed motionvector horizontal and vertical components are set equal to variableshor_max_pic, ver_max_pic, hor_min_pic and ver_min_pic respectively.

Otherwise, the following operations are applied:

-   -   The array deviationMV is set equal to {128, 256, 544, 1120,        2272}.    -   The variables mv_hor_min, mv_ver_min, mv_hor_max and        mv_ver_max(hor_min, ver_min, hor_max and ver_max, used as below)        are derived as following:

hor_min=mv_center[0]−deviationMV[log 2CbWidth−3]  (8-788)

ver_min=mv_center[1]−deviationMV[log 2CbHeight−3]  (8-789)

hor_max=mv_center[0]+deviationMV[log 2CbWidth−3]  (8-790)

ver_max=mv_center[1]+deviationMV[log 2CbHeight−3]  (8-791)

-   -   If hor_min is less than hor_min_pic, the variables hor_min and        hor_max are updated as following:

hor_min=hor_min_pic  (8-788)

hor_max=min(hor_max_pic,hor_min_pic+2*deviationMV[log2CbWidth−3])  (8-790)

-   -   Otherwise, if hor_max is greater than hor_max_pic, the variables        hor_min and hor_max are updated as following:

hor_min=max(hor_min_pic,hor_max_pic−2*deviationMV[log2CbWidth−3])  (8-788)

hor_max=hor_max_pic  (8-790)

-   -   If ver_min is less than ver_min_pic, the variables ver_min and        ver_max are updated as following:

ver_min=ver_min_pic  (8-788)

ver_max=min(ver_max_pic,ver_min_pic+2*deviationMV[log2CbHeight−3])  (8-790)

-   -   Otherwise, if ver_max is greater than ver_max_pic, the variables        ver_min and ver_max are updated as following:

ver_min=max(ver_min_pic,ver_max_pic−2*deviationMV[log2CbHeight−3])  (8-788)

ver_max=ver_max_pic  (8-790)

The output variables hor_max, ver_max, hor_min and ver_min are clippedas follows:

hor_max=Clip3(−2¹⁷,2¹⁷−1,hor_max)  (8-784)

ver_max=Clip3(−2¹⁷,2¹⁷−1,ver_max)  (8-785)

hor_min=Clip3(−2¹⁷,2¹⁷−1,hor_min)  (8-786)

ver_min=Clip3(−2¹⁷,2¹⁷−1,ver_min)  (8-787)

The difference between embodiment 1 and embodiment 2 is in pictureboundaries derivation. In embodiment 1 it is supposed, that there is amargin of 128 (MAX_CU_SIZE) pixels around the picture. The margin sizecan depend on coding tree unit size.

3.2 Boundary Motion Vector Clipping

In EVC it is supposed that each of MV component can be stored using 18bits. To fulfil this general requirement, embodiments of the currentinvention may add clipping to the range [−2¹⁷, 2¹⁷−1] as a final step ofboundary motion vector derivation. To perform this clipping withoutlosing the motion vector magnitude, operations in section 1.4.1.2.3 areperformed in 5-bit precision instead of 9-bit precision. With thesechanges the following changes in general EIF algorithm (section 1.3) areneeded.

-   -   The motion vector mvX is derived as follows:

mvX[0]=(mvBaseScaled[0]+dX[0]*x+dY[0]*y)>>4  (8-758)

mvX[1]=(mvBaseScaled[1]+dX[1]*x+dY[1]*y)>>4  (8-759)

mvX[0]=Clip3(hor_min,hor_max,mvX[0])  (8-760)

mvX[1]=Clip3(ver_min,ver_max,mvX[1])  (8-761)

An operation of “performing a clipping operation on a motion vector of apixel of the coding block to be within a range, to obtain a clippedmotion vector, wherein the range depends on the updated first motionvector range” in the present disclosure corresponds to the equations(8-760) to (8-761).

-   -   The variables xInt, yInt, xFrac and yFrac are derived as        follows:

x Int=xCb+(mvX[0]>>5)+x  (8-762)

yInt=yCb+(mvX[1]>>5)+y  (8-763)

xFrac=(mvX[0])& 31  (8-764)

yFrac=(mvX[1])& 31  (8-765)

3.3 Memory Bandwidth Restrictions Alignment

The specification text examples described above use threshold 81 in theembodiment of operation 6 in section 1.4.1.2.2 for 4×4 EIF subblocks.The section below explains the reasons for using this value of thethreshold.

According to motion vector clipping spread, defined by array deviationMV(section 1.4.1.2.3), the memory bandwidth threshold for uni-predictive8×8 (8×8 is a worst case memory bandwidth, according to arraydeviationMV) affine blocks is equal to

${\frac{\left( {4 + 4 + 8 + 1} \right)^{2}}{8*8} \approx {4.5}},$

that corresponds value 9 for the bi-predictive blocks.

The threshold 81, used in the embodiment of operation 6 in section1.4.1.2.2 for 4×4 EIF subblocks, corresponds to memory bandwidth

$\frac{81}{4*4} \approx 5$

for uni-predictive block that corresponds to the value 10 forbi-predictive blocks.

To align the thresholds used in sections 1.4.1.2.2 and 1.4.1.2.3,embodiments of the current invention may change the threshold in section1.4.1.2.2 from 81 to 72 to achieve memory bandwidth threshold equal to4.5 for uni-predictive and 9 for bi-predictive blocks. With such changememory bandwidth restrictions in sections 1.4.1.2.2 and 1.4.1.2.3 arealigned.

4 Examples of Specification Text of EVC 8.5.3.8 Derivation Process forAffine Subblock Size

Inputs to this process are:

-   -   two variables cbWidth and cbHeight specifying the width and the        height of the luma coding block,    -   the number of control point motion vectors numCpMv,    -   the control point motion vectors cpMvLX[cpIdx], with cpIdx=0 . .        . numCpMv−1 and X being 0 or 1,    -   the prediction list utilization flags predFlagLX, with X being 0        or 1.

Outputs of this process are:

-   -   the size of luma coding subblocks in horizontal direction        sizeSbX and in vertical direction sizeSbY,    -   the number of luma coding subblocks in horizontal direction        numSbX and in vertical direction numSbY,    -   the flag clipMV indicating motion vector clipping type for        blocks processed with EIF.

sizeSbX is set equal to cbWidth, sizeSbY is set equal to cbHeight.

The variables eifCanBeAppliedX and clipMVX are derived as follows for Xbeing 0 and 1:

-   -   eifCanBeAppliedX is set to TRUE    -   clipMVX is set equal to FALSE

The variable eifSubblockSize is set equal to 4.

When predFlagLX is equal to 1, the following applies for X being 0 and1:

-   -   Horizontal change of motion vector dX, vertical change of motion        vector dY and base motion vector mvBaseScaled are derived by        invoking the process specified in clause 8.5.3.9 with the luma        coding block width cbWidth, the luma coding block height        cbHeight, number of control point motion vectors numCpMv and the        control point motion vectors cpMvLX[cpIdx] with cpIdx=0 . . .        numCpMv−1 as inputs.    -   The variable mvWx and mvWy are derived as follows:        -   mvWx=max(abs(dX[0]), abs(dX[1]))        -   mvWy=max(abs(dY[0]), abs(dY[1]))    -   The variable sizeSbXTemp is specificed in Table 8-10 according        to the value of mvWx.    -   The variable sizeSbYTemp is specificed in Table 8-11 according        to the value of mvWy.    -   The variable sizeSbX is modified as follow:        -   sizeSbX=min(sizeSbX, sizeSbXTemp)    -   The variable sizeSbY is modified as follow:        -   sizeSbY=min(sizeSbY, sizeSbYTemp)

TABLE 8-10 Specification of sizeSbXTemp for various input values of mvWxmvWx 0 1 2 3 4 >4 sizeSbX cb Width 32 16 8 8 4

TABLE 8-11 Specification of sizeSbYTemp for various input values of mvWymvWx 0 1 2 3 4 >4 size Sb Y cbHeight 32 16 8 8 4

-   -   The variables eifCanBeAppliedX and clipMVX are modified as        follows:        -   The arrays X[i], Y[i] are derived as follows:            -   X[0]=0            -   X[1]=(eifSubblockSize+1)*(dX[0]+(1<<9))            -   X[2]=(eifSubblockSize+1)*dY[0]            -   X[3]=X[1]+X[2]            -   Y[0]=0            -   Y[1]=(eifSubblockSize+1)*dX[1]            -   Y[2]=(eifSubblockSize+1)*(dY[1]+(1<<9))            -   Y[3]=Y[1]+Y[2]            -   The variable Xmax is set equal to maximum of X[i] for i                is equal 0 . . . 3            -   The variable Xmin is set equal to minimum of X[i] for i                is equal 0 . . . 3            -   The variable Ymax is set equal to maximum of Y[i] for i                is equal 0 . . . 3            -   The variable Ymin is set equal to minimum of Y[i] for i                is equal 0 . . . 3            -   The variable W is set equal to (Xmax−Xmin+(1<<9)−1)>>9            -   The variable H is set equal to (Ymax−Ymin+(1<<9)−1)>>9            -   If (W+2)*(H+2) is greater than 72, the variable clipMVX                is set equal to TRUE            -   If dY[1] is less than ((−1)<<9), then the variable                eifCanBeAppliedX is equal to FALSE            -   Otherwise,                -   If (max(0, dY[1])+Abs(dX[1]))*(1+eifSubblockSize) is                    greater than (1<<9) then the variable                    eifCanBeAppliedX is equal to FALSE.

The variables eifCanBeApplied and clipMV are derived as following:

-   -   eifCanBeApplied=eifCanBeApplied0 & eifCanBeApplied1    -   clipMV=clipMV0 clipMV1

If eifCanBeApplied is equal to FALSE than the variables sizeSbX andsizeSbY are modified as follows:

-   -   sizeSbX=max(8, sizeSbX)    -   sizeSbY=max(8, sizeSbY)

The number of luma coding subblocks in horizontal direction numSbX andin vertical direction numSbY are derived as follows:

-   -   numSbX=cbWidth/sizeSbX    -   numSbY=cbHeight/sizeSbY

8.5.4.3 Interpolation Process for the Enhanced Interpolation Filter

Inputs to this process are:

-   -   a location (xCb, yCb) in full-sample units,    -   two variables cbWidth and cbHeight specifying the width and the        height of the current coding block,    -   horizontal change of motion vector dX,    -   vertical change of motion vector dY,    -   motion vector mvBaseScaled,    -   the selected reference picture sample arrays refPicLX,    -   sample bit depth bitDepth    -   width of the picture in samples pic_width,    -   height of the picture in samples pic_height,    -   clipMV flag specifying MV clipping type,    -   isLuma flag specifying whether luma or chroma is processed.

Outputs of this process are:

-   -   an (cbWidth/SubWidthC)×(cbHeight/SubHeightC) array predSamplesLX        of prediction sample values.

Interpolation filter coefficients T[p] for each fractional sampleposition p equal to xFrac or yFrac are specified in Table 8-16.

The variables hor_max, ver_max, hor_min and ver_min are derived byinvoking the process specified in 8.5.4.5 with a location (xCb, yCb) infull-sample units, two variables cbWidth and cbHeight specifying thewidth and the height of the current coding block, horizontal change ofmotion vector dX, vertical change of motion vector dY, motion vectormvBaseScaled, width of the picture in samples pic_width, height of thepicture in samples pic_height and clipMV flag as input, and hor_max,ver_max, hor_min and ver_min as output.

If isLuma is equal to FALSE, then variables mvBaseScaled, hor_min,hor_max, ver_min, ver_max are modified as follows:

xCb=xCb/SubWidthC  (8-748)

yCb=yCb/SubHeigthC  (8-749)

cbWidth=cbWidth/SubWidthC  (8-750)

cbHeight=cbHeight/SubHeightC  (8-751)

mvBaseScaled[0]=mvBaseScaled[0]/SubWidthC  (8-752)

mvBaseScaled[1]=mvBaseScaled[1]/SubHeightC  (8-753)

hor_min=hor_min/SubWidthC  (8-754)

hor_max=hor_max/SubWidthC  (8-755)

ver_min=ver_min/SubHeightC  (8-756)

ver_max=ver_max/SubHeightC  (8-757)

The variables hor_min, hor_max, ver_min, ver_max before applyingequations (8-754-8-757) represents the updated first motion vectorrange. The variables hor_min, hor_max, ver_min, ver_max after applyingequations (8-754-8-757) represent the range that may be used in anoperation “performing a clipping operation on a motion vector of a pixelof the coding block to be within a range, to obtain a clipped motionvector, wherein the range depends on the updated first motion vectorrange”.

The variables shift0, shift1, offset0 and offset1 are derived asfollows:

shift0 is set equal to bitDepth−8, offset0 is equal to 0,

shift1 is set equal to 12−shift0, offset1 is equal to 2^(shift1−1)

For x=−1 . . . cbWidth and y=−1 . . . cbHeight, the following applies:

-   -   The motion vector mvX is derived as follows:

mvX[0]=(mvBaseScaled[0]+dX[0]*x+dY[0]*y)>>4  (8-758)

mvX[1]=(mvBaseScaled[1]+dX[1]*x+dY[1]*y)>>4  (8-759)

mvX[0]=Clip3(hor_min,hor_max,mvX[0])  (8-760)

mvX[1]=Clip3(ver_mm,ver_max,mvX[1])  (8-761)

An operation of “performing a clipping operation on a motion vector of apixel of the coding block to be within a range, to obtain a clippedmotion vector, wherein the range depends on the updated first motionvector range” in the present disclosure corresponds to the equations(8-760) to (8-761).

The equations below corresponds to the operation of “performingpixel-based motion compensation based on the clipped motion vector”.

-   -   The variables xInt, yInt, xFrac and yFrac are derived as        follows:

x Int=xCb+(mvX[0]>>5)+x  (8-762)

yInt=yCb+(mvX[1]>>5)+y  (8-763)

xFrac=mvX[0]& 31  (8-764)

yFrac=mvX[1]& 31  (8-765)

-   -   The variables A and B are derived as follows:

A=(refPicLX[x Int][yInt]*T[xFrac][0]++refPicLX[xInt+1][yInt]*T[xFrac][1]+offset0)>>shift0  (8-766)

B=(refPicLX[x Int][yInt+1]*T[xFrac][0]++refPicLX[xInt+1][yInt+1]*T[xFrac][1]+offset0)>>shift0(8-767)

-   -   The sample value b_(x,y) corresponding to location (x, y) is        derived as follows:

b _(x,y)=(A*T[yFrac][0]+B*T[yFrac][1]+offset1)>>shift1  (8-768)

The enhancement interpolation filter coefficients eF[ ] are specified as{−1, 10, −1}.

The variables shift2, shift3, offset2 and offset3 are derived asfollows:

-   -   shift2 is set equal to max(bit_depth−11, 0), offset2 is equal to        2^(shift2−1),    -   shift3 is set equal to (6−max(bit_depth−11, 0)), offset3 is        equal to 2^(shift3-1),

For x=0 . . . cbWidth−1 and y=−1 . . . cbHeight, the following applies:

h _(x,y)=(eF[0]*b _(x−1,y) +eF[1]*b _(x,y) +eF[2]*b_(x+1,y)+offset2)>>shift2  (8-769)

For x=0 . . . cbWidth−1 and y=0 . . . cbHeight−1, the following applies:

-   -   predSamplesLX_(L)[x][y]=Clip3(0, (1<<bitDepth)−1,

(eF[0]*h _(x,y−1) +eF[1]*h _(x,y) +eF[2]*b_(x,y−1)+offset3)>>shift3)  (8-770)

TABLE 8-16 Specification of the interpolation filter coefficients T[p]for each fractional sample position p Fractional Interpolation filtersample coefficients position p T[p][0] T[p][1] 0 64 0 1 62 2 2 60 4 3 586 4 56 8 5 54 10 6 52 12 7 50 14 8 48 16 9 46 18 10 44 20 11 42 22 12 4024 13 38 26 14 36 28 15 34 30 16 32 32 17 30 34 18 28 36 19 26 38 20 2440 21 22 42 22 20 44 23 18 46 24 16 48 25 14 50 26 12 52 27 10 54 28 856 29 6 58 30 4 60 31 2 62

8.5.4.5 Derivation of Clipping Parameters for Affine Motion Vector(Variant 1)

Inputs to this process are:

-   -   a location (xCb, yCb) in full-sample units,    -   two variables cbWidth and cbHeight specifying the width and the        height of the current coding block,    -   horizontal change of motion vector dX,    -   vertical change of motion vector dY,    -   motion vector mvBaseScaled,    -   width of the picture in samples pic_width,    -   height of the picture in samples pic_height,    -   clipMV flag specifying MV clipping type.

Outputs of this process are:

-   -   hor_max, ver_max, hor_min and ver_min that denotes the maximum        and minimum allowed motion vector horizontal and vertical        components.

The variables log 2 CbW and log 2 CbH are derived as follows:

log 2CbWidth=Log 2(cbWidth)  (8-774)

log 2CbHeight=Log 2(cbHeight)  (8-775)

The variables hor_max_pic, ver_max_pic, hor_min_pic and ver_min_pic arederived as follows:

hor_max_pic=(pic_width+128−xCb−cbWidth−1)<<5  (8-776)

ver_max_pic=(pic_height+128−yCb−cbHeight−1)<<5  (8-777)

hor_min_pic=(−128−xCb)<<5  (8-778)

ver_min_pic=(−128−yCb)<<5  (8-779)

The variables hor_max_pic, ver_max_pic, hor_min_pic and ver_min_picrepresent the second motion vector range that is used to check whether amotion vector points inside the “first area including referencepicture”.

The center motion vector mv_center is derived as follows:

mv_center[0]=(mvBaseScaled[0]+dX[0]*(cbWidth>>1)+dY[0]*(cbHeight>>1))  (8-780)

mv_center[1]=(mvBaseScaled[1]+dX[1]*(cbWidth>>1)+dY[1]*(cbHeight>>1))  (8-781)

An operation of “obtaining a center motion vector, mv_center of a codingblock” in the present disclosure corresponds to the equations (8-780)and (8-781).

The rounding process for motion vectors as specified in clause 8.5.3.10is invoked with mv_center, rightShift set equal to 4, and leftShift setequal to 0 as inputs and the rounded motion vector is return asmv_center.

If clipMV is equal to FALSE, then the output variables hor_max, ver_max,hor_min and ver_min that denotes the maximum and minimum allowed motionvector horizontal and vertical components are set equal to variableshor_max_pic, ver_max_pic, hor_min_pic and ver_min_pic respectively.

Otherwise, the following operations are applied:

-   -   The array deviationMV is set equal to {128, 256, 544, 1120,        2272}.    -   The variables mv_hor_min, mv_ver_min, mv_hor_max and mv_ver_max        (hor_min, ver_min, hor_max and ver_max, used as below) are        derived as following:

hor_min=mv_center[0]−deviationMV[log 2CbWidth−3](8-788)

ver_min=mv_center[1]−deviationMV[log 2CbHeight−3]  (8-789)

hor_max=mv_center[0]+deviationMV[log 2CbWidth−3]  (8-790)

ver_max=mv_center[1]+deviationMV[log 2CbHeight−3]  (8-791)

An operation of “deriving a first motion vector range for the codingblock based on the center motion vector and a motion vector spread,wherein the motion vector spread depends on a size of the coding block”in the present disclosure corresponds to the equations (8-788)-(8-791).Motion vector spread is represented by a horizontal motion vector spreaddeviationMV[log 2 CbHeight−3] and a vertical motion vector spread [log 2CbHeight−3].

-   -   If hor_min is less than hor_min_pic, the variables hor_min and        hor_max are updated as following:

hor_min=hor_min_pic  (8-792)

hor_max=min(hor_max_pic,hor_min_pic+2*deviationMV[log2CbWidth−3])  (8-793)

-   -   Otherwise, if hor_max is greater than hor_max_pic, the variables        hor_min and hor_max are updated as following:

hor_min=max(hor_min_pic,hor_max_pic−2*deviationMV[log2CbWidth−3])  (8-794)

hor_max=hor_max_pic  (8-795)

-   -   If ver_min is less than ver_min_pic, the variables ver_min and        ver_max are updated as following:

ver_min=ver_min_pic  (8-796)

ver_max=min(ver_max_pic,ver_min_pic+2*deviationMV[log2CbHeight−3])  (8-797)

-   -   Otherwise, if ver_max is greater than ver_max_pic, the variables        ver_min and ver_max are updated as following:

ver_min=max(ver_min_pic,ver_max_pic−2*deviationMV[log2CbHeight−3])  (8-798)

ver_max=ver_max_pic  (8-799)

An operation of “if the first motion vector range is at least partiallypointing outside a first area including a reference picture, updatingthe first motion vector range to be pointing within the first area” inthe present disclosure corresponds to the equations (8-792)-(8-799) andthe corresponding conditions above.

The output variables hor_max, ver_max, hor_min and ver_min are clippedas follows:

hor_max=Clip3(−2¹⁷,2¹⁷−1,hor_max)  (8-800)

ver_max=Clip3(−2¹⁷,2¹⁷−1,ver_max)  (8-801)

hor_min=Clip3(−2¹⁷,2¹⁷−1,hor_min)  (8-802)

ver_min=Clip3(−2¹⁷,2¹⁷−1,ver_min)  (8-803)

An operation of “performing a clipping operation on the updated firstmotion vector range to be within the range [−2¹⁷, 2¹⁷−1]” in the presentdisclosure corresponds to the equations (8-800)-(8-803).

8.5.4.5 Derivation of Clipping Parameters for Affine Motion Vector(Variant 2)

Inputs to this process are:

-   -   a location (xCb, yCb) in full-sample units,    -   two variables cbWidth and cbHeight specifying the width and the        height of the current coding block,    -   horizontal change of motion vector dX,    -   vertical change of motion vector dY,    -   motion vector mvBaseScaled,    -   width of the picture in samples pic_width,    -   height of the picture in samples pic_height,    -   clipMV flag specifying MV clipping type.

Outputs of this process are:

-   -   hor_max, ver_max, hor_min and ver_min that denotes the maximum        and minimum allowed motion vector horizontal and vertical        components.

The variables log 2 CbW and log 2 CbH are derived as follows:

log 2CbWidth=Log 2(cbWidth)  (8-774)

log 2CbHeight=Log 2(cbHeight)  (8-775)

The variables hor_max_pic, ver_max_pic, hor_min_pic and ver_min_pic arederived as follows:

hor_max_pic=(pic_width−xCb−cbWidth−1)<<5  (8-776)

ver_max_pic=(pic_height−yCb−cbHeight−1)<<5  (8-777)

hor_min_pic=(−xCb)<<5  (8-778)

ver_min_pic=(−yCb)<<5  (8-779)

The center motion vector mv_center is derived as follows:

mv_center[0]=(mvBaseScaled[0]+dX[0]*(cbWidth>>1)+dY[0]*(cbHeight>>1))  (8-780)

mv_center[1]=(mvBaseScaled[1]+dX[1]*(cbWidth>>1)+dY[1]*(cbHeight>>1))  (8-781)

The rounding process for motion vectors as specified in clause 8.5.3.10is invoked with mv_center, rightShift set equal to 4, and leftShift setequal to 0 as inputs and the rounded motion vector is return asmv_center.

If clipMV is equal to FALSE, then the output variables hor_max, ver_max,hor_min and ver_min that denotes the maximum and minimum allowed motionvector horizontal and vertical components are set equal to variableshor_max_pic, ver_max_pic, hor_min_pic and ver_min_pic respectively.

Otherwise, the following operations are applied:

-   -   The array deviationMV is set equal to {128, 256, 544, 1120,        2272}.    -   The variables mv_hor_min, mv_ver_min, mv_hor_max and mv_ver_max        are derived as following:

hor_min=mv_center[0]−deviationMV[log 2CbWidth−3]  (8-788)

ver_min=mv_center[1]−deviationMV[log 2CbHeight−3]  (8-789)

hor_max=mv_center[0]+deviationMV[log 2CbWidth−3]  (8-790)

ver_max=mv_center[1]+deviationMV[log 2CbHeight−3]  (8-791)

-   -   If hor_min is less than hor_min_pic, the variables hor_min and        hor_max are updated as following:

hor_min=hor_min_pic  (8-788)

hor_max=min(hor_max_pic,hor_min_pic+2*deviationMV[log2CbWidth−3])  (8-790)

-   -   Otherwise, if hor_max is greater than hor_max_pic, the variables        hor_min and hor_max are updated as following:

hor_min=max(hor_min_pic,hor_max_pic−2*deviationMV[log2CbWidth−3])  (8-788)

hor_max=hor_max_pic  (8-790)

-   -   If ver_min is less than ver_min_pic, the variables ver_min and        ver_max are updated as following:

ver_min=ver_min_pic  (8-788)

ver_max=min(ver_max_pic,ver_min_pic+2*deviationMV[log2CbHeight−3])  (8-790)

-   -   Otherwise, if ver_max is greater than ver_max_pic, the variables        ver_min and ver_max are updated as following:

ver_min=max(ver_min_pic,ver_max_pic−2*deviationMV[log2CbHeight−3])  (8-788)

ver_max=ver_max_pic  (8-790)

The output variables hor_max, ver_max, hor_min and ver_min are clippedas follows:

hor_max=Clip3(−2¹⁷,2¹⁷−1,hor_max)  (8-784)

ver_max=Clip3(−2¹⁷,2¹⁷−1,ver_max)  (8-785)

hor_min=Clip3(−2¹⁷,2¹⁷−1,hor_min)  (8-786)

ver_min=Clip3(−2¹⁷,2¹⁷−1,ver_min)  (8-787)

FIG. 17 is a block diagram illustrating the method according to thepresent disclosure. The method for coding video data using an affinemotion model comprises

-   1701: obtaining a center motion vector of a coding block,-   1702: deriving a first motion vector range for the coding block    based on the center motion vector and a motion vector spread,    wherein the motion vector spread depends on a size of the coding    block,-   1703: if the first motion vector range is at least partially    pointing outside a first area including a reference picture,    updating the first motion vector range to be pointing within the    first area, such that a minimum value and/or a maximum value of the    updated first motion vector range is pointing at the boundary of the    first area, wherein the difference between the maximum value and the    minimum value of the updated first motion vector range is equal to    the minimum of a double value of the motion vector spread and the    size of the first area, and-   1704: performing pixel-based motion compensation based on the    updated first motion vector range.

Examples of the condition that the motion vector range is at leastpartially located outside a boundary of a reference picture are shown inFIGS. 12 and 13 , in which the motion vector range (spread to the leftand right of the central motion vector) is located partially outside theleft boundary of the picture. Similar examples apply to the right, lowerand upper boundaries. The method avoids a significant reduction of themotion vector range near the picture boundaries. The motion vector rangeis here calculated based on a motion vector spread and the referencepicture boundary, instead of based on a motion vector spread the centralmotion vector as in the prior art.

Embodiments of the invention may further provide:

1. A method for performing enhanced interpolation filtering on aboundary of a picture, comprising:

obtaining a motion vector, wherein a target block indicated by themotion vector is a block adjacent to the boundary of the picture;

determining a motion vector range based on the motion vector, whereinthe motion vector range is determined by the size of the target block,and wherein the motion vector range is inside the picture and startsfrom the boundary of the picture; and performing enhanced interpolationfiltering based on the motion vector range.

2. The method of embodiment 1, wherein the picture is a referencepicture of a current block, and wherein the motion vector is a motionvector of the current block.

3. The method of embodiment 1, wherein the picture comprises a margin,wherein the margin is an extended area surrounding an original picture.

4. The method of embodiment 3, wherein a size of the margin depends on amaximum CTU size.

5. The method of embodiment 1, wherein the motion vector range iscalculated based on predefined integer numbers for each preset blockwidth and for each preset block height.

6. A codec comprising processing circuitry for carrying out the methodaccording to any one of embodiments 1 to 5.

7. The method of embodiment 6, wherein the codec comprises an encoder ora decoder.

8. An apparatus for performing enhanced interpolation filtering on aboundary of a picture, comprising:

a memory and a processor coupled to the memory, wherein the processor isconfigured to: obtain a motion vector, wherein a target block indicatedby the motion vector is a block adjacent to the boundary of the picture;

determine a motion vector range based on the motion vector, wherein themotion vector range is determined by the size of the target block, andwherein the motion vector range is inside the

picture and starts from the boundary of the picture; and performenhanced interpolation filtering based on the motion vector range.

9. The apparatus of embodiment 8, wherein the picture is a referencepicture of a current block, and wherein the motion vector is a motionvector of the current block.

10. The apparatus of embodiment 8, wherein the picture comprises amargin, wherein the margin is an extended area surrounding an originalpicture.

11. The apparatus of embodiment 10, wherein a size of the margin dependson a maximum CTU size.

12. The apparatus of embodiment 8, wherein the motion vector range iscalculated based on predefined integer numbers for each preset blockwidth and for each preset block height.

Embodiment 13. A method of coding implemented by a decoding/encodingdevice for coding video data, comprising:

deriving a first motion vector for central point of a affine block,deriving a motion vector spread based on the affine block size (e.g. theaffine block size W×H),

deriving a first motion vector range based on the first motion vectorand the motion vector spread,

deriving a second motion vector range in order to guarantee that MVspoints to a first predefined area,

checking whether the first motion vector range is included into thesecond motion vector range,

if the first motion vector range is not included into the second motionvector range,

-   -   deriving a third motion vector range based on the second motion        vector range and the motion vector spread,

otherwise, set the third motion vector range equal to the first motionvector range, during calculation of motion vectors for the affine blockperform motion vector clipping according to the third range.

Embodiment 14, wherein the first predefined area is area inside thereference picture.

Embodiment 15, wherein the first predefined area is area inside thereference picture with a margin, wherein the margin is an extended areasurrounding the reference picture.

Embodiment 16, wherein the margin depends on a maximum CTU size.

Embodiment 17, wherein the motion vector spread is calculated based oninteger numbers predefined for each possible block width and for eachpossible block height.

According to another aspect, the disclosure relates to a method forinter-prediction of a current image block in a current picture of avideo, the method is used by a decoding/encoding device the methodcomprising:

calculating a subblock size M×N based on affine motion model parametersor based on information from which the affine motion model parameterscan be derived;

in the case that either a subblock width M or a subblock height N issmaller than or equal to a predefined value, performing enhancedbi-linear Interpolation Filter (EIF) motion compensation process,wherein the performing EIF motion compensation process comprises:

deriving a motion vector of a respective subblock of an image block(such as an affine image block) based on the affine motion modelparameters on a P×Q (such as 1×1) subblock basis; and

performing clipping on the motion vector of the subblock, so that theclipped motion vector is in a motion vector range (such as a secondmotion vector range). A motion vector range for the coding block isderived based on the center motion vector of the coding block and a sizeof the coding block, and, if the motion vector range is at leastpartially located outside a boundary of a reference picture, the methodfurther comprise updating the motion vector range to be located withinthe picture, such that a starting value or an end value of the updatedmotion vector range is located at the boundary of the reference picture.

FIG. 18 is a block diagram illustrating a decoder 1500 according to thepresent disclosure. The decoder 1500 comprises one or more processors1510 and a non-transitory computer-readable storage medium 1520 coupledto the one or more processors 1510 and storing instructions forexecution by the one or more processors 1510, wherein the programming,when executed by the one or more processors 1510, configures the decoder1500 to carry out the method according to the present disclosure.

FIG. 19 is a block diagram illustrating an encoder 1600 according to thepresent disclosure. The encoder 1600 comprises one or more processors1610 and a non-transitory computer-readable storage medium 1620 coupledto the one or more processors 1610 and storing instructions forexecution by the one or more processors 1610, wherein the programming,when executed by the one or more processors 1610, configures the decoder1600 to carry out the method according to the present disclosure.

Following is an explanation of the applications of the encoding methodas well as the decoding method as shown in the above-mentionedembodiments, and a system using them.

FIG. 15 is a block diagram showing a content supply system 3100 forrealizing content distribution service. This content supply system 3100includes capture device 3102, terminal device 3106, and may includedisplay 3126. The capture device 3102 communicates with the terminaldevice 3106 over communication link 3104. The communication link mayinclude the communication channel 13 described above. The communicationlink 3104 includes but not limited to WIFI, Ethernet, Cable, wireless(3G/4G/5G), USB, or any kind of combination thereof, or the like.

The capture device 3102 generates data, and may encode the data by theencoding method as shown in the above embodiments. Alternatively, thecapture device 3102 may distribute the data to a streaming server (notshown in the Figures), and the server encodes the data and transmits theencoded data to the terminal device 3106. The capture device 3102includes but not limited to camera, smart phone or Pad, computer orlaptop, video conference system, PDA, vehicle mounted device, or acombination of any of them, or the like. For example, the capture device3102 may include the source device 12 as described above. When the dataincludes video, the video encoder 20 included in the capture device 3102may actually perform video encoding processing. When the data includesaudio (i.e., voice), an audio encoder included in the capture device3102 may actually perform audio encoding processing. For some practicalscenarios, the capture device 3102 distributes the encoded video andaudio data by multiplexing them together. For other practical scenarios,for example in the video conference system, the encoded audio data andthe encoded video data are not multiplexed. Capture device 3102distributes the encoded audio data and the encoded video data to theterminal device 3106 separately.

In the content supply system 3100, the terminal device 310 receives andreproduces the encoded data. The terminal device 3106 could be a devicewith data receiving and recovering capability, such as smart phone orPad 3108, computer or laptop 3110, network video recorder (NVR)/digitalvideo recorder (DVR) 3112, TV 3114, set top box (STB) 3116, videoconference system 3118, video surveillance system 3120, personal digitalassistant (PDA) 3122, vehicle mounted device 3124, or a combination ofany of them, or the like capable of decoding the above-mentioned encodeddata. For example, the terminal device 3106 may include the destinationdevice 14 as described above. When the encoded data includes video, thevideo decoder 30 included in the terminal device is prioritized toperform video decoding. When the encoded data includes audio, an audiodecoder included in the terminal device is prioritized to perform audiodecoding processing.

For a terminal device with its display, for example, smart phone or Pad3108, computer or laptop 3110, network video recorder (NVR)/digitalvideo recorder (DVR) 3112, TV 3114, personal digital assistant (PDA)3122, or vehicle mounted device 3124, the terminal device can feed thedecoded data to its display. For a terminal device equipped with nodisplay, for example, STB 3116, video conference system 3118, or videosurveillance system 3120, an external display 3126 is contacted thereinto receive and show the decoded data.

When each device in this system performs encoding or decoding, thepicture encoding device or the picture decoding device, as shown in theabove-mentioned embodiments, can be used.

FIG. 16 is a diagram showing a structure of an example of the terminaldevice 3106. After the terminal device 3106 receives stream from thecapture device 3102, the protocol proceeding unit 3202 analyzes thetransmission protocol of the stream. The protocol includes but notlimited to Real Time Streaming Protocol (RTSP), Hyper Text TransferProtocol (HTTP), HTTP Live streaming protocol (HLS), MPEG-DASH,Real-time Transport protocol (RTP), Real Time Messaging Protocol (RTMP),or any kind of combination thereof, or the like.

After the protocol proceeding unit 3202 processes the stream, streamfile is generated. The file is outputted to a demultiplexing unit 3204.The demultiplexing unit 3204 can separate the multiplexed data into theencoded audio data and the encoded video data. As described above, forsome practical scenarios, for example in the video conference system,the encoded audio data and the encoded video data are not multiplexed.In this situation, the encoded data is transmitted to video decoder 3206and audio decoder 3208 without through the demultiplexing unit 3204.

Via the demultiplexing processing, video elementary stream (ES), audioES, and subtitle may be generated. The video decoder 3206, whichincludes the video decoder 30 as explained in the above mentionedembodiments, decodes the video ES by the decoding method as shown in theabove-mentioned embodiments to generate video frame, and feeds this datato the synchronous unit 3212. The audio decoder 3208, decodes the audioES to generate audio frame, and feeds this data to the synchronous unit3212. Alternatively, the video frame may store in a buffer (not shown inFIG. Y) before feeding it to the synchronous unit 3212. Similarly, theaudio frame may store in a buffer before feeding it to the synchronousunit 3212.

The synchronous unit 3212 synchronizes the video frame and the audioframe, and supplies the video/audio to a video/audio display 3214. Forexample, the synchronous unit 3212 synchronizes the presentation of thevideo and audio information. Information may code in the syntax usingtime stamps concerning the presentation of coded audio and visual dataand time stamps concerning the delivery of the data stream itself.

If subtitle is included in the stream, the subtitle decoder 3210 decodesthe subtitle, and synchronizes it with the video frame and the audioframe, and supplies the video/audio/subtitle to a video/audio/subtitledisplay 3216.

Embodiments of the present invention is not limited to theabove-mentioned system, and either the picture encoding device or thepicture decoding device in the above-mentioned embodiments can beincorporated into other system, for example, a car system.

Mathematical Operators

The mathematical operators used in this application are similar to thoseused in the C programming language. However, the results of integerdivision and arithmetic shift operations are defined more precisely, andadditional operations are defined, such as exponentiation andreal-valued division. Numbering and counting conventions generally beginfrom 0, e.g., “the first” is equivalent to the 0-th, “the second” isequivalent to the 1-th, etc.

Arithmetic Operators

The following arithmetic operators are defined as follows:

-   -   + Addition    -   − Subtraction (as a two-argument operator) or negation (as a        unary prefix operator)    -   * Multiplication, including matrix multiplication    -   x^(y) Exponentiation. Specifies x to the power of y. In other        contexts, such notation is used for superscripting not intended        for interpretation as exponentiation.    -   / Integer division with truncation of the result toward zero.        For example, 7/4 and −7/−4 are truncated to 1 and −7/4 and 7/−4        are truncated to −1.

Used to denote division in mathematical equations where no truncation orrounding is intended.

$\frac{x}{y}$

Used to denote division in mathematical equations where no truncation orrounding is intended.

$\sum\limits_{i = x}^{y}{f(i)}$

The summation of f(i) with i taking all integer values from x up to andincluding y.

-   -   Modulus. Remainder of x divided by y, defined only for integers        x and y with x>=0 x % y and y>0.

Logical Operators

The following logical operators are defined as follows:

-   -   x && y Boolean logical “and” of x and y    -   x∥y Boolean logical “or” of x and y    -   ! Boolean logical “not”    -   x? y:z If x is TRUE or not equal to 0, evaluates to the value of        y; otherwise, evaluates to the value of z.

Relational Operators

The following relational operators are defined as follows:

-   -   > Greater than    -   >= Greater than or equal to    -   < Less than    -   <= Less than or equal to    -   == Equal to    -   != Not equal to

When a relational operator is applied to a syntax element or variablethat has been assigned the value “na” (not applicable), the value “na”is treated as a distinct value for the syntax element or variable. Thevalue “na” is considered not to be equal to any other value.

Bit-Wise Operators

The following bit-wise operators are defined as follows:

-   -   & Bit-wise “and”. When operating on integer arguments, operates        on a two's complement representation of the integer value. When        operating on a binary argument that contains fewer bits than        another argument, the shorter argument is extended by adding        more significant bits equal to 0.    -   | Bit-wise “or”. When operating on integer arguments, operates        on a two's complement representation of the integer value. When        operating on a binary argument that contains fewer bits than        another argument, the shorter argument is extended by adding        more significant bits equal to 0.    -   {circumflex over ( )} Bit-wise “exclusive or”. When operating on        integer arguments, operates on a two's complement representation        of the integer value. When operating on a binary argument that        contains fewer bits than another argument, the shorter argument        is extended by adding more significant bits equal to 0.    -   x>>y Arithmetic right shift of a two's complement integer        representation of x by y binary digits. This function is defined        only for non-negative integer values of y. Bits shifted into the        most significant bits (MSBs) as a result of the right shift have        a value equal to the MSB of x prior to the shift operation.    -   x<<y Arithmetic left shift of a two's complement integer        representation of x by y binary digits. This function is defined        only for non-negative integer values of y. Bits shifted into the        least significant bits (LSBs) as a result of the left shift have        a value equal to 0.

Assignment Operators

The following arithmetic operators are defined as follows:

-   -   = Assignment operator    -   ++ Increment, i.e., x++ is equivalent to x=x+1; when used in an        array index, evaluates to the value of the variable prior to the        increment operation.    -   −− Decrement, i.e., x−− is equivalent to x=x−1; when used in an        array index, evaluates to the value of the variable prior to the        decrement operation.    -   +=Increment by amount specified, i.e., x+=3 is equivalent to        x=x+3, and x+=(−3) is equivalent to x=x+(−3).    -   −=Decrement by amount specified, i.e., x−=3 is equivalent to        x=x−3, and x−=(−3) is equivalent to x=x−(−3).

Range Notation

The following notation is used to specify a range of values:

-   -   x=y . . . z x takes on integer values starting from y to z,        inclusive, with x, y, and z being integer numbers and z being        greater than y.

Mathematical Functions

The following mathematical functions are defined:

${{Abs}(x)} = \left\{ \begin{matrix}x & ; & {x>=0} \\{- x} & ; & {x < 0}\end{matrix} \right.$

-   -   A sin(x) the trigonometric inverse sine function, operating on        an argument x that is in the range of −1.0 to 1.0, inclusive,        with an output value in the range of −π÷2 to π÷2, inclusive, in        units of radians    -   A tan(x) the trigonometric inverse tangent function, operating        on an argument x, with an output value in the range of −π÷2 to        π÷2, inclusive, in units of radians

${A\tan 2\left( {y,x} \right)} = \left\{ \begin{matrix}{A{\tan\left( \frac{y}{x} \right)}} & ; & {x > 0} \\{{A{\tan\left( \frac{y}{x} \right)}} + \pi} & ; & {{x < 0}\&\&{y>=0}} \\{{A{\tan\left( \frac{y}{x} \right)}} - \pi} & ; & {{x < 0}\&\&{y < 0}} \\{+ \frac{\pi}{2}} & ; & {{x==00}\&\&{y>=0}} \\{- \frac{\pi}{2}} & ; & {otherwise}\end{matrix} \right.$

Ceil(x) the smallest integer greater than or equal to x.

Clip1_(Y)(x)=Clip3(0,(1<<BitDepth_(Y))−1,x)

Clip1_(C)(x)=Clip3(0,(1<<BitDepth_(C))−1,x)

${{Clip}3\left( {x,y,z} \right)} = \left\{ \begin{matrix}x & ; & {z < x} \\y & ; & {z > y} \\z & ; & {otherwise}\end{matrix} \right.$

Cos(x) the trigonometric cosine function operating on an argument x inunits of radians.

Floor(x) the largest integer less than or equal to x.

${{GetCurrMsb}\left( {a,b,c,d} \right)} = \left\{ \begin{matrix}{c + d} & ; & {{b - a}\ >={d/2}} \\{c - d} & ; & {{a - b} > {d/2}} \\c & ; & {otherwise}\end{matrix} \right.$

Ln(x) the natural logarithm of x (the base-e logarithm, where e is thenatural logarithm base constant 2.718 281 828 . . . ).

Log 2(x) the base-2 logarithm of x.

Log 10(x) the base-10 logarithm of x.

${{Min}\left( {x,y} \right)} = \left\{ \begin{matrix}x & ; & {x<=y} \\y & ; & {x > y}\end{matrix} \right.$${{Max}\left( {x,y} \right)} = \left\{ \begin{matrix}x & ; & {x>=y} \\y & ; & {x < y}\end{matrix} \right.$

Round(x)=Sign(x)*Floor(Abs(x)+0.5)

${{Sign}(x)} = \left\{ \begin{matrix}1 & ; & {x > 0} \\0 & ; & {x==0} \\{- 1} & ; & {x < 0}\end{matrix} \right.$

-   -   Sin(x) the trigonometric sine function operating on an argument        x in units of radians    -   Sqrt(x)=√{square root over (x)}    -   Swap(x,y)=(y, x)    -   Tan(x) the trigonometric tangent function operating on an        argument x in units of radians

Order of Operation Precedence

When an order of precedence in an expression is not indicated explicitlyby use of parentheses, the following rules apply:

-   -   Operations of a higher precedence are evaluated before any        operation of a lower precedence.    -   Operations of the same precedence are evaluated sequentially        from left to right.

The table below specifies the precedence of operations from highest tolowest; a higher position in the table indicates a higher precedence.

For those operators that are also used in the C programming language,the order of precedence used in this Specification is the same as usedin the C programming language.

TABLE Operation precedence from highest (at top of table) to lowest (atbottom of table) operations (with operands x, y, and z) “x++”, “x− −”“!x”, “−x” (as a unary prefix operator) x^(y)${``{x*y}"},{``{x/y}"},{``{x \div y}"},{``\frac{x}{y}"},{``{x\% y}"}$${``{x + y}"},{{``{x - y}"}\left( {{{as}a{two}}‐{{argument}{operator}}} \right)},{``{\sum\limits_{i = x}^{y}{f(i)}}"}$“x << y”, “x >> y” “x < y”, “x <= y”, “x > y”, “x >= y” “x = = y”, “x !=y” “x & y” “x | y” “x && y” “x | | y” “x ? y : z” “x . . . y” “x = y”,“x += y”, “x −= y”

Text Description of Logical Operations

In the text, a statement of logical operations as would be describedmathematically in the following form:

   if( condition 0)   statement 0  else if( condition 1 )   statement 1 ...   else /* informative remark on remaining condition */   statementn may be described in the following manner:  ... as follows /... thefollowing applies:  - If condition 0, statement 0  - Otherwise, ifcondition 1, statement 1  - ...

-   -   Otherwise (informative remark on remaining condition), statement        n

Each “If . . . Otherwise, if . . . Otherwise, . . . “statement in thetext is introduced with” . . . as follows” or “ . . . the followingapplies” immediately followed by “If . . . ”. The last condition of the“If . . . Otherwise, if . . . Otherwise, . . . ” is always an“Otherwise, . . . ”. Interleaved “If . . . Otherwise, if . . .Otherwise, . . . “statements can be identified by matching” . . . asfollows” or “ . . . the following applies” with the ending “Otherwise, .. . ”.

In the text, a statement of logical operations as would be describedmathematically in the following form:

if( condition 0a && condition 0b )  statement 0 else if( condition 1a || condition 1b )  statement 1 ... else  statement n may be described inthe following manner: ... as follows /... the following applies: - Ifall of the following conditions are true, statement 0:  - condition 0a - condition 0b - Otherwise, if one or more of the following conditionsare true, statement 1:  - condition 1a  - condition 1b - ... -Otherwise, statement n

In the text, a statement of logical operations as would be describedmathematically in the following form:

   if( condition 0)   statement 0  if( condition 1 )   statement 1 maybe described in the following manner:  When condition 0, statement 0 When condition 1, statement 1.

Although embodiments of the invention have been primarily describedbased on video coding, it should be noted that embodiments of the codingsystem 10, encoder 20 and decoder 30 (and correspondingly the system 10)and the other embodiments described herein may also be configured forstill picture processing or coding, i.e. the processing or coding of anindividual picture independent of any preceding or consecutive pictureas in video coding. In general only inter-prediction units 244 (encoder)and 344 (decoder) may not be available in case the picture processingcoding is limited to a single picture 17. All other functionalities(also referred to as tools or technologies) of the video encoder 20 andvideo decoder 30 may equally be used for still picture processing, e.g.residual calculation 204/304, transform 206, quantization 208, inversequantization 210/310, (inverse) transform 212/312, partitioning 262/362,intra-prediction 254/354, and/or loop filtering 220, 320, and entropycoding 270 and entropy decoding 304.

Embodiments, e.g. of the encoder 20 and the decoder 30, and functionsdescribed herein, e.g. with reference to the encoder 20 and the decoder30, may be implemented in hardware, software, firmware, or anycombination thereof. If implemented in software, the functions may bestored on a computer-readable medium or transmitted over communicationmedia as one or more instructions or code and executed by ahardware-based processing unit. Computer-readable media may includecomputer-readable storage media, which corresponds to a tangible mediumsuch as data storage media, or communication media including any mediumthat facilitates transfer of a computer program from one place toanother, e.g., according to a communication protocol. In this manner,computer-readable media generally may correspond to (1) tangiblecomputer-readable storage media which is non-transitory or (2) acommunication medium such as a signal or carrier wave. Data storagemedia may be any available media that can be accessed by one or morecomputers or one or more processors to retrieve instructions, codeand/or data structures for implementation of the techniques described inthis disclosure. A computer program product may include acomputer-readable medium.

By way of example, and not limiting, such computer-readable storagemedia can comprise RAM, ROM, EEPROM, CD-ROM or other optical diskstorage, magnetic disk storage, or other magnetic storage devices, flashmemory, or any other medium that can be used to store desired programcode in the form of instructions or data structures and that can beaccessed by a computer. Also, any connection is properly termed acomputer-readable medium. For example, if instructions are transmittedfrom a website, server, or other remote source using a coaxial cable,fiber optic cable, twisted pair, digital subscriber line (DSL), orwireless technologies such as infrared, radio, and microwave, then thecoaxial cable, fiber optic cable, twisted pair, DSL, or wirelesstechnologies such as infrared, radio, and microwave are included in thedefinition of medium. It should be understood, however, thatcomputer-readable storage media and data storage media do not includeconnections, carrier waves, signals, or other transitory media, but areinstead directed to non-transitory, tangible storage media. Disk anddisc, as used herein, includes compact disc (CD), laser disc, opticaldisc, digital versatile disc (DVD), floppy disk and Blu-ray disc, wheredisks usually reproduce data magnetically, while discs reproduce dataoptically with lasers. Combinations of the above should also be includedwithin the scope of computer-readable media.

Instructions may be executed by one or more processors, such as one ormore digital signal processors (DSPs), general purpose microprocessors,application specific integrated circuits (ASICs), field programmablelogic arrays (FPGAs), or other equivalent integrated or discrete logiccircuitry. Accordingly, the term “processor,” as used herein may referto any of the foregoing structure or any other structure suitable forimplementation of the techniques described herein. In addition, in someaspects, the functionality described herein may be provided withindedicated hardware and/or software modules configured for encoding anddecoding, or incorporated in a combined codec. Also, the techniquescould be fully implemented in one or more circuits or logic elements.

The techniques of this disclosure may be implemented in a wide varietyof devices or apparatuses, including a wireless handset, an integratedcircuit (IC) or a set of ICs (e.g., a chip set). Various components,modules, or units are described in this disclosure to emphasizefunctional aspects of devices configured to perform the disclosedtechniques, but do not necessarily require realization by differenthardware units. Rather, as described above, various units may becombined in a codec hardware unit or provided by a collection ofinteroperative hardware units, including one or more processors asdescribed above, in conjunction with suitable software and/or firmware.

1. A method for coding video data, comprising: obtaining a center motionvector of a coding block; deriving a first motion vector range for thecoding block based on the center motion vector and a motion vectorspread, wherein the motion vector spread depends on a size of the codingblock; if the first motion vector range is at least partially pointingoutside a first area including a reference picture, updating the firstmotion vector range to point within the first area, such that a minimumvalue a maximum value of the updated first motion vector range ispointing at a boundary of the first area, wherein a difference betweenthe maximum value and the minimum value of the updated first motionvector range is equal to a minimum of a double value of the motionvector spread and a size of the first area; and performing pixel-basedmotion compensation based on the updated first motion vector range. 2.The method of claim 1, wherein the motion vector spread is representedby a horizontal motion vector spread or a vertical motion vector spread,the horizontal motion vector spread is derived based on a width of thecoding block, and the vertical motion vector spread is derived based onthe height of the coding block.
 3. The method of claim 2, wherein thehorizontal motion vector spread is represented by deviationMV[log 2CbWidth−3], and the vertical motion vector spread is represented bydeviationMV[log 2 CbHeight−3], wherein deviationMV is a motion vectordeviation, and cbWidth and cbHeight respectively represent the width andthe height of the coding block.
 4. The method of claim 1, wherein thefirst motion vector range is represented by a first motion vector (MV)horizontal component range or a first MV vertical component range, thefirst MV horizontal component range comprises a first minimum MVhorizontal component value and a first maximum MV horizontal componentvalue, and the first MV vertical component range comprises a firstminimum MV vertical component value and a first maximum MV verticalcomponent value.
 5. The method of claim 4, further comprising: derivinga second motion vector range based on a size of a picture comprising thecoding block, wherein the second motion vector range is represented by asecond MV horizontal component range or a second MV vertical componentrange, the second MV horizontal component range comprises a secondminimum MV horizontal component value and a second maximum MV horizontalcomponent value, and the second MV vertical component range comprises asecond minimum MV vertical component value and a second maximum MVvertical component value.
 6. The method of claim 5, wherein updating thefirst motion vector range to point within the first area comprises: ifthe first minimum MV horizontal component value is less than the secondminimum MV horizontal component value, setting an updated value of thefirst minimum MV horizontal component value equal to the second minimumMV horizontal component value, and deriving an updated value of thefirst maximum MV horizontal component value based on a sum of the secondminimum MV horizontal component value and a double value of a horizontalmotion vector spread.
 7. The method of claim 5, wherein updating thefirst motion vector range to point within the first area comprises: ifthe first maximum MV horizontal component value is greater than thesecond maximum MV horizontal component value, setting an updated valueof the first maximum MV horizontal component value; equal to the secondmaximum MV horizontal component value, and deriving an updated value ofthe first minimum MV horizontal component value based on a subtractionvalue of the second maximum MV horizontal component value and a doublevalue of a horizontal motion vector spread.
 8. The method of claim 5,wherein updating the first motion vector range to point within the firstarea comprises: if the first minimum MV vertical component value is lessthan the second minimum MV vertical component value, setting an updatedvalue of the first minimum MV vertical component value equal to thesecond minimum MV vertical component value, and deriving an updatedvalue of the first maximum MV vertical component value based on a sum ofthe second minimum MV vertical component value and a double value of avertical motion vector spread.
 9. The method of claim 5, whereinupdating the first motion vector range to point within the first areacomprises: if the first maximum MV vertical component value is greaterthan the second maximum MV vertical component value, setting an updatedvalue of the first maximum MV vertical component value equal to thesecond maximum MV vertical component value, and deriving an updatedvalue of the first minimum MV vertical component value based on asubtraction value of the second maximum MV vertical component value anda double value of a vertical motion vector spread.
 10. The method ofclaim 1, wherein if the first motion vector range is at least partiallypointing outside a left boundary of the first area, updating variableshor_min and hor_max, representing a first motion vector (MV) horizontalcomponent range of the first motion vector range, as:hor_min=hor_min_pic, hor_max=min (hor_max_pic, hor_min_pic+2*horizontalmotion vector spread); wherein hor_min indicates an updated firstminimum MV horizontal component, and hor_max indicates an updated firstmaximum MV horizontal component; wherein hor_min_pic indicates a secondminimum MV horizontal component of a second MV horizontal componentrange of a second motion vector range, and hor_max_pic indicates asecond maximum MV horizontal component of the second MV horizontalcomponent range of the second motion vector range, and wherein thesecond motion vector range depends on a size of a picture comprising thecoding block.
 11. The method of claim 1, wherein if the first motionvector range is at least partially pointing outside a right boundary ofthe first area, updating variables hor_min and hor_max, representing afirst motion vector (MV) horizontal component range of the first motionvector range, as: hor_min=max (hor_min_pic, hor_max_pic−2*horizontalmotion vector spread), hor_max=hor_max_pic; wherein hor_min indicates anupdated first minimum MV horizontal component, and hor_max indicates anupdated first maximum MV horizontal component; wherein hor_min_picindicates a second minimum MV horizontal component of a second MVhorizontal component range of a second motion vector range, andhor_max_pic indicates a second maximum MV horizontal component of thesecond MV horizontal component range of the second motion vector range,and wherein the second motion vector range depends on a size of apicture comprising the coding block.
 12. The method of claim 1, whereinif the first motion vector range is at least partially pointing outsidean upper boundary of the first area, updating variables ver_min andver_max, representing a first motion vector (MV) vertical componentrange of the first motion vector range, as: ver_min=ver_min_pic,ver_max=min (ver_max_pic, ver_min_pic+2*vertical motion vector spread);wherein ver_min indicates an updated first minimum MV verticalcomponent, and ver_max indicates an updated first maximum MV verticalcomponent; wherein ver_min_pic indicates a second minimum MV verticalcomponent of a second MV vertical component range of a second motionvector range, and ver_max_pic indicates a second maximum MV horizontalcomponent of the second MV horizontal component range of the secondmotion vector range, and wherein the second motion vector range dependson a size of a picture comprising the coding block.
 13. The method ofclaim 1, wherein if the first motion vector range is at least partiallylocated outside a lower boundary of the first area, updating variablesver_min and ver_max, representing a first motion vector (MV) verticalcomponent range of the first motion vector range, as: ver_min=max(ver_min_pic, ver_max_pic−2*vertical motion vector spread),ver_max=ver_max_pic; wherein ver_min indicates an updated first minimumMV vertical component of the first MV vertical component range, andver_max indicates an updated first maximum MV vertical component of thefirst MV vertical component range; wherein ver_min_pic indicates asecond minimum MV vertical component of a second MV vertical componentrange of a second motion vector range, and ver_max_pic indicates asecond maximum MV horizontal component of the second MV horizontalcomponent range of the second motion vector range, and wherein thesecond motion vector range depends on a size of a picture comprising thecoding block.
 14. The method of claim 1, wherein a minimum or maximumvalue of a horizontal component of the updated first motion vector rangeis pointing at a left or right boundary of the first area, respectively;or a minimum or maximum value of a vertical component of the updatedfirst motion vector range is pointing at an upper or lower boundary ofthe first area, respectively.
 15. The method of claim 1, wherein thefirst area comprises the reference picture and an extended areasurrounding the reference picture.
 16. The method of claim 15, wherein asize of the extended area is 128 pixels.
 17. The method of claim 1,further comprising: performing a clipping operation on the updated firstmotion vector range to be within a range [−2¹⁷, 2¹⁷−1]; whereinperforming the pixel-based motion compensation comprises: performing thepixel-based motion compensation based on the updated and clipped firstmotion vector range.
 18. The method of claim 1, wherein performing thepixel-based motion compensation comprises: performing a clippingoperation on a motion vector of a pixel of the coding block to be withina range, to obtain a clipped motion vector, wherein the range depends onthe updated first motion vector range; and performing the pixel-basedmotion compensation based on the clipped motion vector.
 19. A decoder,comprising: one or more processors; and a non-transitorycomputer-readable storage medium coupled to the one or more processorsand storing instructions, which when executed by the one or moreprocessors, cause the decoder to perform the method according toclaim
 1. 20. An encoder, comprising: one or more processors; and anon-transitory computer-readable storage medium coupled to the one ormore processors and storing instructions, which when executed by the oneor more processors, cause the encoder to perform the method according toclaim 1.